We have put together a short survey to capture your feedback in terms of what BT can do when you experience home Wi-Fi issues. We would appreciate it if you could take a couple of minutes to complete a short survey. Read more from here, Fix my home Wi-Fi
@Haddaway97 Then take it up with the person who bought it or the developers. Other than that there is no solution that can be offered here other than what google can tell you if you look for "extend wired network".
If you don't own the house have you contacted the person who does and ask why they did not pay the additional cost to get the developer to install ethernet connection in all the rooms wired access to a panel beside the hub - as shown in @pippincp post of openreach installations
And again as everyone else has said this has nothing to do with BT RETAIL the homeowner has cut costs
"The facts are that BT guarantee fibre all over the house and WiFi in every room. Yet it only works in 2 rooms of the house. That's a BT Retail guarantee. They don't provide that and offer no solution to fix it."
Are you sure about that? Even on complete wifi the guarantee is reliable wifi in every room. Are you on complete wifi?