i would honestly just sit them down and go for it (if you feel comfortable), explain that this is how you identify and that you care about how they feel? that’s how i did it with my suitemates last year and they ended up being really supportive. i also dunno ur exact situation but i hope this was helpful nonetheless :3
if it’s hard for you, you can tell them in pieces over time. might start as presenting how you want to around them. and eventually maybe tell them your new name or pronouns. doesn’t have to be in that order! whatever you’re most comfortable with first, tell them when you’re ready. and you don’t have to have an explanation or anything.