Is the extender roughly half way between the router and the device your trying to improve? Wi-Fi can be impacted by things like wall construction, thick walls, a neighbour using the same channel etc. I’d start by scanning for someone using the same channel or trying a series of channels to see if a specific channel gives a better result. You could also try a speed tester app at different locations to see where the speeds really drop off significantly. What sort of speeds are you expecting and get connected at the router?
