First, you need to see if the bell is brass plated or solid brass.
If solid, Id start with a super fine steel wool, to check what is needed to smooth surface and any discoleration
Next is a trip to harbor freight...Youll need loose stitched and hard stiched muslim buffing wheels...I believe they make a back, and brown cutting tripoli and green polishing rouge....not red, bad stuff.
A buffing will bring to new, and youll need to spray seal when done, and after an alcohol cleaning.