As DND9000 said, sounds like clutch bearing.
see part #8 here
https://www.diyspareparts.com/parts/stihl/diagrams/fs-90-r/c881d664-4251-4f36-8e47/
dont forget to remove the circlip on the shaft side.
Pretty easy to do.
remove screws that hold the bell housing off, then remove circlip, push out shaft, Bearing may or may not come out, if it doesent, just drift it out of the housing, just make sure there is not an external circlip in the housing, been a while since I last did one and cant remember, sorry.
was a pretty common bearing too and cheap from any bearing/ tractor place.