When you accidentally sell your weapon you will get in-game currency, this makes it an irreversible action on our end.
After selling your weapon we will not be able to help you retrieve it or cancel the transaction. If we were to intervene, it would make it unfair for the other players who performed these actions intentionally.
Chances are, the item will drop again during play, most probably at an even higher item power.
To avoid selling an item by accident, you can lock it. Tap on the item and then on the padlock symbol, which will turn from grey to white. You will see that the “Sell” button is now greyed out and it is not possible to sell the item by accident anymore. To unlock the item, simply click the padlock icon again.