Continuous WiFi issues

[Paparory]

Fibre connection and Sky SR213 Router with poor WiFi 

ZOOM and Ms Teams freezes and reports poor internet connection.

On the fibre install the engineer insisted that the router had to go in one corner of the house, this is the opposite corner and downstairs from room used as office. How can I sort this?

In contrast the previous Virgin install allowed the router in the middle of the house.

Also, I am unable to reach websites on my phone, it hangs, and I have to use mobile data. This happens most often in the morning. How can I sort this?