Here's a challenge: A person comes to you to try and change the highness or lowness of their voice. For a transgender person, this can be one of the hardest issues to deal with. It's a daunting piece to the puzzle of figuring out how to express oneself. They can have a lot of discomfort and frustration about their voices, which can cause a feeling of disconnect between their assigned sex and their gender identity.
There are now surgeries available (e.g., feminization laryngoplasty surgery) that can alter the vocal cords. But besides being expensive, there are risks involved in surgery, like permanent damage to the vocal cords. Vocal cord surgery can diminish the lower end of the vocal register, but it doesn't teach people how to use their voices, so they may continue to speak using the same "habits" as before. Voice therapy is often recommended after this sort of surgery.
But before resorting to surgery or hormones, I always recommend trying other routes first.
Tips for Training Transgender Voices
First of all, voice training can be a very intimate process, so move carefully, slowly, and without judgment. It can take time, and change can be very gradual and subtle. Tell your clients this will be a time for experimentation and create a safe space for that. They'll probably need a minimum of weekly sessions for a while because changing one's voice is one of the hardest things to do!
Male to female
If you're working with a male-to-female transsexual client, it helps if the voice she is starting out with is a tenor voice. Some high tenors don't even sound that different from a female already. Using scales and vocal exercises is a good way to start, since people tend to be more willing to try different sounds when it's "just an exercise."
I think of times when I, myself, have found a very "thinned out" sound or feel to my voice in order to make it easier to get up into the high notes of a song. It is possible to learn how to draw out the higher frequencies or the lower frequencies in our speech. We can choose to hit a note with deepness and power, or we can produce that same note with a lighter feel.
Using a "funny" quality, a little witchy, with a wider vowel can be one way of achieving a lighter feel. Another way is to try a "heady" vowel, like a wee or woo, which moves the voice toward a headier quality. Then, try having her talk, saying "really" or "right" using a higher voice than she is used to, with a more expressive quality. Lip trills are good, or try humming on a pitch and moving it up like an elevator. With this, she can explore a different feeling for speaking.
Read and recite sentences, ones she might say in real life, using her feminine voice. After training, including altering the movement of the mouth, trans women are capable of producing significantly higher frequencies.
Remember, we don't want to throw the voice completely out of balance so that it tires out easily. I've heard women who are not transgender actually try to deepen their sound when they have very high voices, and this can tire out the voice. We want the voice to have vocal balance and not be overly weighted toward the upper or lower side. You have to have a working chest voice and head voice no matter who you are and what gender you are. So, like any singer taking voice lessons, they must discover chest and head and try to relax the outer muscles not to work too hard.
Keep in mind that there is no ONE way for a woman to sound because no two human voices will ever be the same. It's also a misconception that raising the pitch of the voice is the only aspect that makes it female. There are also certain speaking habits women might use more than men (and vice versa), such as phrasing things as a question rather than a statement, or using less staccato, more flowing sentences. These are habits we are raised with in certain cultures, from birth, which are not necessarily genetic.
Female to male
For female-to-male transsexual clients, vowel changes can help attain a deeper, richer quality. As opposed to a "bright" sound, a rounder sound can be attained by dropping the jaw or narrowing the vowels a bit. Altos will have an easier time because their voices are already deeper.
One of the biggest issues with low notes is that vocal cords tend to open and lose adduction as we get into the deepest parts of our voices. So work into the bottom of his voice using speaking exercises, but get him to find the right cord adduction and resonance that will help to keep the cords closing together lower. A very bright sound up in the front of the mouth can help do this as you are beginning to bring the voice down low.
These exercises should help to expand one's "comfort zone" of where the voice wants to be. With the right work, they will find more tools so they can feel good communicating and connecting with others.