Information on how to connect Trezor with MyCrypto can be found in this article.
If you have trouble connecting your Trezor with MyCrypto, please make sure your configuration meets the following points:
If you can't see desired address with your funds after exporting public keys from Trezor to MyCrypto, it means you are accessing a different wallet. Either you have a different recovery seed stored in your Trezor or you are entering a different passphrase.
To access a wallet that includes the address you want to add to MyCrypto, you need to use the same combination of recovery seed and passphrase as you used when you generated this address for the first time.
You can find more information on issues with passphrase in this article.
If MyCrypto preventing you from spending your funds (signing a transaction), this actually might be caused when the (appropriate) private key is missing. These private keys for signing transactions are derived from the combination of the recovery seed stored on Trezor device and passphrase (if enabled and used). Hence, if a different recovery seed and/or a different passphrase is used then the private key differs and cannot be used. In such case, previously generated wallets/accounts in third-party apps would become watch-only wallets without the possibility of spending the funds.
To be able to successfully sign a transaction, you need to use the right combination of recovery seed and passphrase for the address from which the transaction is being made.