Likely the fastest way would be to use a text editor like Visual Studio Code, open the main
Assets directory there (
File - Open Folder..) so that it's searchable. Then search and replace usage of the Skeleton shader guid string:
, guid: 1e8a610c9e01c3648bac42585e5fc676,
and replace it with usage of the
URP/Spine/Skeleton shader guid:
, guid: b2f45941d9f4fe9479ce1aebb9d63fbf,
Note that the
, is used here to only replace usage of the guid, not where it's declared, which is the
.meta file next to the shader.
As always be sure to backup your project first so that you can revert any mistakes that happen.