Once a cryptocurrency transaction has been sent, its transaction is irreversible and cannot be cancelled. This rule does not apply just to SatoshiWallet, but this is how cryptocurrencies are designed at its core, and it applies to all cryptocurrencies and wallet providers out there.
If you want to reverse the transaction, you will need to contact the person, website or business, that you sent the transaction to, and provide them with your unique Transaction ID, which is like a receipt or proof of payment.
Let them know that you sent the transaction to them and that you would like to have it refunded. The Transaction ID can be found by tapping on the wallet that the transaction was sent out of. Then tap on the transaction that you want to copy and have refunded by the other party, and open the "Advanced Transaction Data" information. At the transaction data screen, you will see the Transaction ID, along with information such as the number of confirmations that this transaction has received.
This transaction data is the relevant link to send to the other party, which shows proof that payment was made.