This info. from Trezor security.
On August 1st, a group of users and some businesses are planning to implement a non-compatible upgrade to the network, raising the blocksize limit to 8MB and removing SegWit. As this upgrade does not have a wide backing of the network, this “hard fork” would split the Bitcoin network in two. As a result, we will be left with the Bitcoin with activated SegWit (through BIP91/BIP141) and its clone, dubbed Bitcoin Cash.
As this is a chain-split, Bitcoin Cash will share its entire transaction history with Bitcoin up until the point of the split, with the history diverging after the split. This means that for whatever amount of bitcoins you had before the split on your TREZOR, you will end up having that same amount of Bitcoin Cash. Bitcoin and Bitcoin Cash essentially become two separate currencies.
To gain access to your Bitcoin Cash coins, your action will be required after August 1st, and only if you want Bitcoin Cash.
What do I need to do to claim my Bitcoin Cash?
We will provide an interface, accessible from TREZOR Wallet, where you can access and safely claim your Bitcoin Cash coins. You will be prompted by TREZOR Wallet once you select “Bitcoin Cash” in the currency selector. After this, you can use Bitcoin and Bitcoin Cash side by side.
No action is necessary on the original Bitcoin chain.
Full story can be found here: https://blog.trezor.io/bitcoin-cash-hard-fork-chain-split-safe-guide-abbe3e9c553f