Modem mode - where to plug in my V6 box?

Hi - I'm getting a TP Link mesh wifi kit (DECO X10 AX1500) and have a few questions. Searching on here I've learned about switching my Hub 3 into modem mode and setting up the new router. I've also learned that my phone connection can remain in the Hub 3 port which will still work in modem mode.

However, I haven't been able to find out what to do with the ethernet cable that currently connects the Hub to the V6 box. Will that also stay where it is, or does it need to plug into the TP Link router instead?

Non-techy so thanks for any simple language replies!