Welcome to this user forum. @Frizzybee
Try the usual fixes for the home hub, in this order.
factory reset the home hub.
Then turn Smart Setup off.
Then separate and rename the SSIDs.
This is a common problem for new customers and a forum search would brought up the suggestion made by @Keith_Beddoe Which normally solve your problem
If the OP has a Smart Hub2, the bands can't be split. Despite being the source of many problems, the Hub designers think they know better and have removed the facility to split the bands.
Which version of the hub are you using
if unsure then post stats. Advanced settings then technical log information
If you have managed to split the bands, your devices will now have 2 entries for your hub, the original SSID and the re-named 5Ghz SSID if they are dual band. If you can't see the renamed 5Ghz SSID on the device it will be because it is only single band.