Return of BRP after naturalization

Hello!
I wonder if someone can help me with the following:
My friend applied for British citizenship and he has finally received his British passport. He was ready to return his biometric residence permit (he had been here for 5 years with Tier 2) but he cannot find it and he thinks it got lost when he moved houses. What can he do about it? He is scared he can get fined. Is there any Home Office any contact details where he can inquire about it?
Thanks in advance.