How to verify your seed owns a particular public address?

Hi, I am trying to help out an old friend, who is some distance from me, who has had a slight bungle with his Trezor/Metamask wallet some time ago. He is fairly computer basic, but to rule out one thing before I travel to help him I just wanted to know if there was a way to do the following:

He has two accounts, a Trezor seed phrase, and also the Trezor seed phrase with the passphrase/extra word (secret wallet as they call it). He can see the etherscan public eth wallet address with the funds in it on chain, but tells me he connected it to a new computer or metamask and can no longer see the funds anywhere.

He cannot seem to locate them in metamask, Trezor suite, but providing everything he is telling me is correct, the receive address was derived from that Trezor.

Question is: How can you verify that a known 0x-public address is owned by your seed phrase/ private key?