While both Opera and Opera GX are closed, in both "C:\Users\yourusername\AppData\Roaming\Opera Software" and "C:\Users\yourusername\AppData\Local\Opera Software", you can:
Right-click the "Opera GX Stable" folder, choose "copy", right-click in a blank spot in the "Opera Software" folder and choose "paste" to create a backup of the folder named "Opera GX Stable - Copy".
Delete the "Opera Stable" folder.
Rename the "Opera GX Stable" folder to "Opera Stable".
Then, when you start regular Opera you should have everything.