Please make sure that your Trezor is connected to your computer.
You can then go ahead and select the Trezor option in the Safe Multisig application:
You will get asked about which derivation path to use. If you don't know what that is, the default selection will work. Click "Connect".
You will now be guided through Trezor's screens to connect you Trezor.
Eventually, back in the Gnosis Safe, you need to select which account you want to use.
After clicking "Done" you can now sign and execute Safe transactions.
Currently, it is not possible to set the gas price of a transaction execution from within the Safe Multisig. The gas price is set by the signer wallet, which often allow users to modify the gas price manually in order to achieve the preferred execution speed. However, Trezor does not let their users manually set the gas price. In most cases, this is not an issue, but sometimes the gas estimation is not correct leading to a failed transaction due to an out of gas error
Trezor via Metamask
While we do not recommend it, you can also import your Trezor account into Metamask and use this to sign in the Safe Multisig. Here’s how to do this.