don't try to teach your grandma to suck eggs

The phrase "don't try to teach your grandma to suck eggs" is an idiomatic expression that advises against attempting to teach someone who is experienced or knowledgeable in a particular area something they already know or have expertise in. It implies that it is pointless or unnecessary to teach someone something they are already highly skilled or knowledgeable about. The phrase can be used to signal that one should avoid giving unsolicited advice or instruction to someone who is more experienced or knowledgeable than oneself.