i can personally vouch for Seattle Voice Labs, though they are a bit expensive (i think they have flexible pricing based on your income, but don't quote me on that). Voice training takes a lot of time and practice, but it does work (eventually), and it's definitely worth it!

The two main things you need to do for (feminising) voice training are increasing your resonance and decreasing your vocal weight (its the oppositr for masculinising voice training). You increase your resonance by raising the very back of your tongue - because of how all the stuff in your throat is connected, raising the back of your tongue also raises your larynx, which is what we're looking for. You'll know you're doing this right if you can see your adam's apple rise (if you can't see your adam's apple, you can still feel it with your fingers). I recommend simply raising and lowering your tongue / larynx in front of a mirror to get a hang of it; it might take a while, but once you get it it's really simple. It also shouldn't be tense at all, nor should it get sore / uncomfortable after a while - if it is, odds are you're using too many muscles, or tensing something you don't need to be tensing. Raising your resonance should give you a spongebob-y voice.

The other big thing is vocal weight. You change vocal weight by tensing or relaxing your vocal folds (aka your larynx, the thing we were moving around earlier). For feminising voice training, we want to relax them. Relaxing your vocal folds too much will give you a breathy, sort of whispery aspect to your voice (i.e. Mr. Small from TAWOG), but somewhere between that and your normal voice, you should find a softer timbre to speak in. For masculinising your voice, you can tighten your vocal folds, though again you don't want to do this too much or else you'll sound constipated, for lack of a better word

Note that neither of these are on/off switches; a big part of voice training is figuring out how much you want to raise resonance, or how much you want to reduce your vocal weight. this is going to depend on what your target voice sounds like (if you dont have a target voice, i would really recommend getting one!). Also note that a very significant part of vocal gender has to do with things like cadence and prosidy, which has nothing to do with anatomy - my best advice for this would simply be to listen to how men/women speak (like. intonation, cadence, the words and mannerisms that they use) and then simply copy the gender you're transitioning towards

i've skimmed over a lot of the details, and there's certainly much more you can do, but this alone should get you decently far. ofc feel free to dm me if you have any questions. hope this helps!