I have two on steam, one empty, the other not... and I connected the empty one.

It is possible to change gog connect steam account?

Contact support.

Try to contact support and explain your situation, maybe with some goodwill they will do it. Officially it's not possible and mentioned on GOGs Conncect homepage (left side, last paragraph): "You can connect only one Steam account with your GOG.com library. This process is permanent – choose wisely!"

He chose.. poorly.

Ouch. They do warn you that it's permanent and it's probably so you wouldn't just collect stuff across accounts not your own.. But since the account is empty and you didn't redeem anything yet, perhaps support will show you kindness. Good luck!

Support contact.

I doubt it's possible You made your decision upon connecting the accounts.

You may need to wait a until Monday for a response from support, because there are fewer of them working during the weekend. I hope that they agree to help you undo that accident. Good luck.

Thanks everyone.

I didn t realize the error.

I'll contact support.