Hello my name is ***** ***** I will help You.
Does the agreement allow you to levy a charge for this?
Then sadly no you can not charge.
Your right to charge comes from the terms of the agreement and if the agreement does not allow you to charge for this then you can not.
You have no power under the contract to charge for it.
I am sorry if this is not the answer you want and certainly not the one I want to give you, but I have a duty to be honest.
Can I clarify anything for you about this today please?
You ask for confirmation in writing that tenant has left and can then change the locks. But you can't charge for that.
I am sorry. Alex