Honestly your best friend will be YouTube, and discord. I’d suggest joining avatar creator discords bc sometimes they post helpful tips and tricks. For now I have the link to the YouTube creator that has helped me do unity edits.
https://youtube.com/@lucindabeskins?si=MdcIgr8gehvVo7m5
For blender, you can look at these videos.
(How to sculpt in blender) https://youtu.be/-bbuyh00hbQ?is=lItPk7FhhXX0Zshp
(How to make seamless neck merge) https://youtu.be/ACnApsra81E?is=Jscmbz0fV8lkllNk
And then I have this creator who I assume has been everyone’s go to for over the past two years that’s helped many people get into avatar creation. I advise you follow along with her tutorial, even if it is 2 years old, it shouldn’t be too different when you use the updated blender.
https://youtube.com/@askamberofficial?si=6TC6o43Qz9lUrPHx
In the end, you can always ask for help in Google or ask around in discord servers. Or even ask me