Removing / adjusting soft close toilet seat

I wonder whether anyone can help. About 5 years ago I replaced our cloakroom toilet and chose a Tavistock Structure Back to the wall toilet with soft-close lid. Since I installed it the soft close hasn't been that effective, so during lock-down I thought I'd remove the seat and see if there was any adjustment.

To remove the lid there are 2 buttons at inside edge of hinges that you press. The problem is that one of the buttons wont move.

I e-mailed Tavistock to try and get there help, but there answer was:

"There isn’t any adjustment on this seat and if the button is stuck, there isn’t another easy way to remove this seat apart from removing from the underside of the pan." Obviously the toilet is fully enclosed so you cant get to the underside of the pan.

Can anyone offer any advice please both in removing the lid and if there is anyway of improving the soft close hinge. I wonder if another manufacture's soft-close cylinder dampers could be used in their place?