Do I need anything installed locally to use GitHub other than what I already use for development?

Not necessarily. You can do it all through the GitHub web interface. However, using git on your local machine can make things easier: you can use your own choice of editor, save your work part way through, run local tests, etc.

Do I need to get permission/acceptance from the maintainer?

Not up front, no. When you make the pull request the owner of the repo will be alerted to it and will either accept it or respond with feedback prior to accepting. If you refer to the issue that has already been raised in the PR text that will help.

There is some general guidance here but essentially the process is

1. Obtain a github account if you don't already have one.
2. Fork the repo
3. Make changes to your fork
4. Raise the pull request

1. Obtain a github account if you don't already have one.
2. Fork the repo
3. Make changes to your fork
4. Raise the pull request

OK...

I already had a github account and have forked the repo, made the changes...

What's the right way to test it?
I've installed git but I've not used that for the PR. I've done it all online. The only file that needed changing was /Module/Starter/Somple.pm

I could just make the same change in my local copy installed from CPAN and test that. Although that would work for this simple change, it doesn't seem a good or scalable method of testing changes.

The common workflow is to create a fork, clone the repository to a working copy on your machine, make the changes, and run the tests (usually something like make test, or dzil test, etc.) For simple modules, prove -vl is often enough.
map{substr$_->[0],$_->[1]||0,1}[\*||{},3],[[]],[ref qr-1,-,-1],[{}],[sub{}^*ARGV,3]

• https://docs.github.com/en/get-started/quickstart
• https://github.com/features/code-review