How do I remove old, yellowed, sealant from ceramic tile countertop?

Do you know what the sealant is?

i would use ...orange stripper super gentle...should be able to scrape off ...almost immediatley

try Goo Gone NOT Goof off( chemicals will damage porcelain) Goo Gone has oil base and won't harm surfaces except painted ones use the squeeze bottle stuff easier than spray to get exactly where u need it and no waste. Loosen sealant with PK and get the GG right under /behind the sealant let sit for 5min then pull off the sealant This is not a 123 job and in order to replace sealant so it doesn't crack or peel the area has to be cleaned and free of all moisture, dust, oils etc.

i would try a magic eraser if that doesnt work try clorox clean up