Close Opera and Opera GX.
Then, in Windows Explorer (File Explorer) (with extensions and hidden items set under View -> Show), browse to "C:\Users\yourusername\AppData\Roaming\Opera Software".
In that "Opera Software" folder, rename the "Opera GX Stable" folder to "Opera GX Stable old". Then, rename (or copy if you want to keep your regular Opera data) the "Opera Stable" folder to "Opera GX Stable".
Then, do the same thing in "C:\Users\yourusername\AppData\Local\Opera Software"
Then, your regular Opera profile will be tranferred/copied to Opera GX. You can then start Opera GX and customize and Opera-GX-Specific settings.