i'm more interested in investigating the change address which was allocated for the fees of the mixing service.
Change address?
Are you referring to bc1qaamrxr0s469970e9m9tea4d9ssa7vfd7uq9cqk?
The fund sent to change has nothing to do the fee.
When you make a bitcoin transaction, the remaining balance of selected UTXOs goes to your change address.
You should be the one who controls that address.