As a user, you do not need to do anything to prepare for the Ethereum merge. Your accounts and coins will not be affected and sending/recieving will work like before.

The Ethereum merge is a backend change done by the node operator (currently Etherscan for the BitBoxApp). The node operator will update to the latest Ethereum client in order to support the merge.

How will Ethereum proof-of-work (ETHW) work after the merge?

A minority of miners have expressed their intention to continue the proof of work chain of Ethereum. This will be a different chain to the majority Ethereum chain that will continue as proof of stake. Every Ethereum holder will get the equivalent amount of ETHW after the fork.

Will the BitBox support ETHW?

Since ETHW is just a change in the chainID, it is technically possible to send and receive ETHW to and from the BitBox02. However this will need to be done by a third party app that supports the BitBox02 and will support ETHW (either through Rabby or MyEtherWallet). There are no plans to add ETHW to the BitBoxApp.

Currently, neither Rabby nor MyEtherWallet support ETHW. Therefore it is not currently possible to send ETHW from the BitBox02. We recommend waiting for one of these wallets to support ETHW before attempting to recover them on your own.

How to access ETHW from seed? (NOT SECURE AND NOT RECOMMENED!)

If you must access your ETHW, you can import your seed words into a wallet that is compatible with ETHW. Such as Metamask (you can manually add the ETHW network to Metamask using this guide). This is strongly NOT recommended since your wallet will no longer be secured by the BitBox02. Any coins on that wallet (including your BTC, ETH, LTC, ERC20 tokens etc.) will be vulnerable. If you import your seed into another wallet, we strongly recommend you move all your coins to another secure wallet (such as another BitBox02 or hardware wallet) before importing the seed.
Again, we recommend waiting for Rabby or MyEtherWallet to support ETHW instead of importing your seed into another wallet.
Listed below are some useful articles to learn more about ETH2, staking and the merge.