You can either replace the needle seat itself but if you don’t have a new seat to hand (or you already did it) you can wind some PTFE tape around the body of the needle seat. Not sure where in the world you are but here in the UK it’s also referred to as plumbers tape. That will make the fit tighter and the seat wont lift out with the needle.
which sampler do you have? you can replace the seat adapter as well...
This is the plastic part the seat sits in....
For the G1313A/G1329A it is pn G1313-43204
and for the wellplate G1367X- pn G1367-43200