How to fix the internal bolts from the toilet seat without mounting?

Hello. Most likely you are asking for a one-piece Arcus toilet. The model is quite peculiar, it looks beautiful and aesthetically pleasing, but in terms of repair it is very difficult.

All options, except for replacing the cover with a new one with a normal mount, will be temporary and will bring only discomfort during operation. To replace it, you will have to remove the toilet, change and fix a new cover from underneath, then put everything back. I attach a photo and a diagram for an illustrative example.