HGG Community Forums

You will have to be logged in to your main account. Then go to Stable Overview and select Account and Stable Management.

The second option there is Request Account Merging. That's where you'll need to be. You'll find the instructions for doing the merger there.

Also if the newer account contain mostly benefits from welcome achievements then it may not be mergeable as is. They have gotten stricter to keep the game balanced. I ran into that issue recently. It's a resolveable problem, there were just additional steps that changed what was possible for me to do.