My car is saying low refrig A/C Off.Can I fix this myself? on 1998 Cadillac Eldorado

My husband is a corpsman & while in Afghanistan I drove this car and I have never had this problem, but it is a 98', it only had one other owner & we had this car since 2010. Is this an easy fix? I hope so because we need to save money. Someone please help!

Asked by for the 1998 Cadillac Eldorado