Normally, plastic "yellowing" is caused by sunlight. Perhaps the frig was left open during storage, exposing the interior to the sun. It will not harm anything, I'd leave it as-is, other than normal cleaning.
Some harsh chemicals will eat into the plastic, if you do use one, do so on a small out-of-sight test area. I do know Westly's Bleach White sidewall tire cleaner will remove yellowing from plastic, and in the process removes that damaged plastic, leaving a stippled surface which is much harder to keep clean. I'll never do that again.
2000 Winnebago Ultimate Freedom USQ40JD
, ISC 8.3 Cummins 350, Spartan MM Chassis. USA 1SG, retired;PPA,Good Sam Life member."We the people are the rightful masters of both the Congress and the Courts - not to overthrow the Constitution but to overthrow men who pervert theConstitution. "Abraham Lincoln"