First, you must first find out why the other party declared your patent invalid.
Second, on the basis of finding out the invalid reasons, break the other party's invalid reasons one by one;
Third, don't give evidence yet. The other party declares your patent invalid, and the other party bears the first burden of proof. You should first look at what flaws the other party has, and let the other party's evidence and reasons be invalid first. You should take offense as defense, not defense first. If the other party's invalid reason is not established, no proof is needed. Only after the first proof is completed will the burden of proof be transferred to you. Remember, attack is defense! You can't just defend.