Another way to phrase this question is, "How do multiple developers use the same code base in their work?"
Selenium automation is just using an open source library to set up testing. It's not any different to what your developers do in your teams codebase. The process and setup are the same.
What does that look like?
- Ensure the Selenium project is set up in a code repository (Github, Bitbucket, etc)
- Ensure any work QA/Test automation engineers have setup a story to work in (usually in Jira). This can be a separate ticket for automation only or you can attach the work to the same story developers use.
- Create a new branch in git to attach to the story you created.
- In git or your code IDE/Editor, pull down that new branch.
- Create any automation tests you need.
- Submit a pull request when you're done coding. Here, you'll want the other Selenium contributors to review each others work.
- Once the pull request is approved, you'll merge your code the main branch.
Following standard developer coding practices will ensure that multiple people can work in the same codebase to do Selenium automation coding.