scratching my head on this one to move wifi connection

so i have my pi hole connected via 2.4ghz ( only supports that? ) its a pi zero 2w

when i did the install, i first turned off the 5ghz on my three uk 5g home hub and it just would not connect after 3 goes and had to put in the three hub.

working

but the problem is strange, if i connect anything to the three hub wireless, i get speeds from 15mb to 50mb. Yet i have a halo mesh system in the flat and speed test any of them and i get 200-500mb

how do i change the connect without spending yet more hours re doing everything