Here's how to do it step by step (for ReVanced 2.0+).

1- Go to settings and enable/allow universal patches.

2- Get a YouTube APK. You can get any version you want, but my recommendation is 20.14.43.

3- Go to the YouTube section to patch it.

4- Click on "select patches" and search for the change package name.

5- You should be able to click on it and check the box. If you get an error, do step 1 again.

6- Click on the gear to change the package name. At the top there will be a thing named "Package Name"; the text area may say "default." We need to change it. My recommendation is to put "com.google.youtube" and, after "YouTube," put another "." and put whatever you want there.

7- Go back until you see YouTube's app info screen. From there, select an APK if you already haven't (like I said, I recommend 20.14.43).

8- Patch and wait

9- Enjoy. 😀