You can and must switch the white Swisscom router to bridge mode, after which the Swisscom part only functions as a modem... And the Asus router then takes over all functions including WLAN!!! Everything is faster and more stable... The Asus routers are TOP!!!! I have the ROG with 8 antennas a great router super fast and stable 0 crashes and TOP speed even on the 2.4Ghz WLAN to 1GBit and 2* 5Ghz to a total of 5.3 GBit simultaneously.... Costs more but it's worth it ;-,))))

You must be able to operate the existing modem in bridge mode, then a WLAN can be set up with the ASUS router that is significantly faster than with the Swisscom part. You must ask Swisscom whether the Swisscom modem can be operated in this way.

Actually
You only need the Swisscom Box, which has the modem function and is also a router. So you can set up your own W-lan with this box alone without an additional router. Otherwise ask Swisscom.