Modem mode new router and Frequency

Irish Gunner

I have a virgin media hub 4 and I want to put it into modem mode and use asus router.

However no option to switch to modem mode in settings so may ring virgin to switch it to ip4, take it they can do this?

However frequency are not split between 2.4 and 5.

Before I start process do I need to split frequency on virgin router before before putting into modem mode or do I put it into modem mode and then split frequency on new router