How to replace the back gasket

Hi all :) My Galaxy Watch 4 Classic 46mm unfortunately got water damaged. I believe the battery died and am changing it. But checking the whole watch for further damage if found, that the back gasket desintegrated.

I want to change it and bought a new gasket of ebay.

Now my biggest issue is, that I don´t know how to attach and seal the new gasket. Even after some googling, searching youtube and even asking AI I haven´t found any usable instructions on that.

Could somebody please explain to me, how to attach and seal the new gasket?

I can provide photos if necessary.

Thank you in advance

With appreciation, Manfred