The standard one is from a channel called, literally, TransVoiceLessons. There are other trans women led voice training lessons, Zheanna is just like the standard one. There's plenty of otherwise cis guys that give instructions on how to do "the girl voice" (for trolling omegle or something???), but personally for me following a trans woman's lessons on how to feminize helped more because they generally had a better idea of what I wanted out of it. I didn't want to sound like a mousy 15 year old for a laugh, I was okay with a deeper but still unmistakably femme adult voice and I wanted to use it every day in every situation so it had to last and be sustainable.

You don't have to pay for lessons but having a coach or a program is quite nice if you can afford it. I used a program to track my pitch but vocal feminization isn't all about pitch (it's actually much more to do with other aspects), still was nice to be able to track my progress with something objective regardless.

It can be hard to start. We've all felt it, you're in good company including any trans woman who has a voice you like and who transitioned post puberty (little easier for her if she got a head start lol). You can absolutely do it, getting started is pure head game. When I started I couldn't train because of the amxiety unless I was completely alone in the house, roommate gone and my ex gone lol. It was much easier after I started training and trying stuff out with a friend who was much bolder and wanted to compare