1. Setup your trezor on mytrezor website.
2. Download the electrum-dash wallet from the dash website under downloads.
3. Plug in trezor then launch electrum-dash.
4. Choose create new wallet and select hardware wallet and click next.
5. Trezor should be selected so just click next again.
6. On the server connection screen just accept the default auto connect option and click next.
7. It should ask to enter the trezor pin, enter it then click ok and it will create your dash wallet.
I'd post links but can't yet, sorry.