I’m admittedly kinda bad about this myself, but I’ve found it works to just, do it at the start of a semester. Especially if your class has introductions on the first day it’s really easy to do it then, at least if you can push past the discomfort. If your school uses your deadname maybe talk to the prof after class to make sure they get it. (My friends recommended emailing but I’ve heard horror stories about that so I haven’t done it ever)

In the case of the girl you want to be friends with though, you could just try talking to her to be friendlier (smalltalk can work, eventually it’ll develop into something closer to an actual discussion as you know each other better) then come out when you’re already friends. It’s what I did with the cool trans people in my classes and they’re my best friends now.

As for your other friends that you can’t introduce your gf to, try to come out to several of them at once while making sure that friends who already know are in the group too. It makes it much easier when you have that bit of backup to work with.

None of these are really the ideal way to do it though, I still haven’t figured that out myself so I stress over it anytime I need to come out to people.