What should I do to be forgiven for my sin after taking clothes from my uncle's bag, with whom we are estranged, and I cannot tell him for fear of being accused of theft?

You must hasten to repent to Allah Almighty for stealing, betraying trusts, and severing ties of kinship. Your remorse for what you have done indicates that repentance expiates what came before it, but sincere repentance is necessary, fulfilling the شرعي (shar'i) conditions. Repentance is not complete unless what was taken is returned to its owner, either directly or indirectly, unless the owner willingly pardons it. It will be easier for you to reconcile with your uncle and communicate with him. If you do that and fulfill what Allah has obligated upon you, everything will become easy for you, as Allah Almighty says: "And whoever fears Allah - He will make for him a way out."