Any advice on clearing up a chronic ear infection in one ear of a seven year old Cocker Spaniel?

Ear infections are hard to get rid of in long eared dogs. You'll need to clean the ear with an ear cleaning fluid, using a cotton ball. Be careful not to go too far into the ear canal. You will probably need to see the vet to get the proper drops to put into the ear once it's cleaned out. You have to be consistent with the cleaning and drops or it's a lost cause. Good luck.