Wet room floor drain to waste pipe

[Cassh]

Help! Our wet room was fitted by the previous owners, we had a leak into room below which made us investigate and we can see that there is a seal where to pipes meet that has partially popped out of place and is visible inside the pipe. After monitoring we know it’s leaking through here. I apologise for the long post But as a non-plumber it’s difficult for me to describe.
It’s an oblong shower trap, when you lift the metal cover there’s an oval hair trap that slots in. If you lift this out I can see the whole thing is one moulded piece that ends in a round pipe (internal diameter seems to be 104mm). This joins (via the slipped seal) a bottom piece that has a small outlet to the right (around 40mm) which must meet the waste outlet somewhere under the floor.
I can’t replace it as it’s all tiled in. I don’t know any way to pop the seal back on, is it possible?
Only other option I can think of is to create a sealed route within the existing openings, a pipe that fits snug inside the top section above the dodgy seal and reduces to connect directly into the outlet on the right but I don’t know what materials or sizes to look for.
Any advice or suggestions would be welcomed, thanks

 

[opps]

Can't you cut a hole in the ceiling below it to access the connection?

 

[Cassh]

@opps possibly as a last resort if all else fails but it’s a painted smooth plaster ceiling and I don’t have the budget to pay a plasterer to re-do. The water damage was right at the edge so I can fix that with filler.

 

[jeff the gasman]

Cut a neat hole in the ceiling with a multitool
Remove board, repair leak and replace board with timber supports added.
Fill, sand and repaint.

 

[opps]

Cut a neat hole in the ceiling with a multitool
Remove board, repair leak and replace board with timber supports added.
Fill, sand and repaint.

Agreed. If done neatly, it will require filler, sanding and painting rather than plastering. The bit of plasterboard (assuming that it is plasterboard) will go back up.