Apple Watch Series 7 ringtone

You're welcome. If it helps, there never has been a way to select a different or custom ringtone on the Apple Watch, and we are currently on Series 7, so it would be out of character if it happened now.

That is currently not an option. This is a user to user support forum and Apple does not participate here. If you wish to provide feedback to Apple regarding a change you would like to see, a change you didn’t like, or report a bug, then use the feedback link here, Feedback - iPhone - Apple