How to swap from a sub-address

hi there,
I’m trying to make a swap from a sub-address. My main public address is already added to Metamask, but I want to make a swap from an address that is also associated with the wallet. I want to add the public address to the wallet, and then make the swap/ confirm on the same hardware wallet that’s associated with my primary address. So if my Trezor has a primary address of …6876 and one of the sub-addresses is …7391, how do I swap coins on the…7391 address (on ethereum mainnet)?
thanks!
Chris