Is there any way to manually set the birthday for another team member?

You can even do it in batches now! Learn how to do so here.

There is! As an admin, you can go to the web app, and find Settings > Members to locate the person you want to set the birthday for. Click their name to open their profile. You'll see a summary like this:

Click "Edit" then to open up their user settings. You can change them in there.

Got additional questions? Submit a new ticket.