can't update a git submodule from github web interface

Short answer - not currently possible to do it from the web interface. Discussion about this is at https://github.com/orgs/community/discussions/15079#discussioncomment-9292900

The same terminal commands are needed as referenced in the earlier post, https://hnsws.blogspot.com/2025/04/change-submodule-for-git-repository.html

In my case, since I'm using github actions to build OpenSpace (which I don't have commit access to), what I can do is to just 

cd whichever/submodule/parentdirectory

rm -Rf submoduledirectory

git clone https://fresh.git.subdirectory.url submoduledirectory
cd submoduledirectory

git checkout whatever-branch

before the configure and build steps. Or, of course, if just updating the branch is needed, only the git checkout line would be needed.