There is no button for this. The delivery address is set at checkout, and nothing in the app lets you change it afterwards.
That is worth stating plainly rather than sending you looking. What you have instead are two routes, and both close when the parcel leaves.
Route one: ask the seller
Message them from the order, immediately, with the full correct address.
This works far more often than people expect. A seller who has not packed yet is editing one line before printing a slip, and most would much rather do that than deal with a parcel coming back.
Say it in one message: the order, the wrong address, the right address. Do not bury it in a conversation.
Route two: cancel and buy again
Available while the order can still be cancelled — before it ships. A cash-on-delivery order can be cancelled until it ships too.
For an auction win this is a bad idea: cancelling a win does not give you another chance at the item, and the win is gone. Route one is the only sensible route for a win.
For a buy-now item it is clean, if the stock is still there — cancel, order again with the right address, and the refund of the first follows.
Once it has shipped
Neither route exists. The parcel is with a courier, and Metzee cannot redirect it.
What sometimes works: call the courier yourself with the tracking number. Some will hold a parcel at a hub for collection or accept a redirect within the same city. That is their policy, not ours, and asking costs nothing.
If it is already on its way to the wrong place
Tell the seller anyway, so they know before it comes back. A parcel refused or returned to sender is resolvable; one that was delivered to a wrong address you did not mention is much harder.
The thing that prevents all of this
Check the address on the payment screen rather than after. It is shown before you pay, and ten seconds there saves the whole of the above. I entered the wrong address.
More: how to track an order, when will my order be sent, how pickup works.