I don't really understand why would it be some change returning?
That's how bitcoin transactions work.
Every time you receive a transaction, you receive a UTXO.
Let's say you have received two transactions. In each of them you received 0.5 BTC. Now you have two UTXOs and you want to spend 0.75 BTC.
As you UTXOs must be spent completely, you have to use both UTXOs. So you make a transaction with two inputs and two outputs.
One of receiving addresses is owned by the recipient and the other on is your own address which receives the remaining balance of UTXOs.
Do you know how I can do to complete or cancel this transaction ?
The network is so congested now.
If you are not in hurry, just wait. Your transaction will be confirmed.
If you are in hurry, you can bump the fee.