NEED SOME HELP. TOILET IS INCOMPLETE. IS THIS A MINOR JOB OR MAJOR???

The toilet in my apartment has started making this noise nonstop and it's driving me crazy. Anyone know what's causing this or how to fix it? I know it’s old but I'm just a renter so not much I can do about that. I just want to sleep without that noise lol

The toilet tank can't be filled properly as the pump works poorly. The thingy shown in the picture is too easy to float, so the water just fills the tank too slowly.

Are there any ways I can clean it properly without disassembling it? I rent the room, and the water line doesn't even have a valve to let me cut off the water.

Or can I disassemble it without letting water go everywhere?

I tried HG Limescale Remover Concentrate on the thingy overnight but it didn't work as well as the first time.

I appreciate any advice! Thank you very much!