When you see that message you need to click on the cancel button. Once you cancel your save, you are sent back to your edit screen… that edit screen is the screen with the issue so you need to cancel out from that screen too, and then re-click on the edit button to start again. If you then attempt to save and you get the message again, you need to hit cancel twice again and continue in this manner until you can save without seeing any overwrite messages.
A basic use case has the following workflow:
Click edit → open edit screen
Add your name to the edit screen
click Save
If you see the overwrite message, click cancel
4a) → If you cancelled, you are now back at the edit screen that (if saved) will overwrite others, so you need to click cancelagain
if you had to cancel, start again from #1
If you didn’t see any overwrite message, click save and your name is added without overwriting anyone and you are done editing the wiki.