

Repeaters don’t work, especially on newer Wifi clients. You need a proper Mesh system to cover a larger area. Probably going to run you $300-$500USD for a 3 AP kit.
You’ll need to put that junky AP they sent you from the ISP into Passthrough Mode, hook up the new AP from the Mesh system as your new router, then just place the other new APs in mesh mode as you want them.
If you have multiple other APs and some wires Ethernet ports in the house, you could switch those into AP Mode, plug them into Ethernet, and they’ll act as extensions of your main router as a hacky mesh as well. The problem with this route is that if they are all different WiFi versions and standards, you’ll get a bit of wonky behavior here and there, but it will work.
















Edited to a bit more. See my other comment.
We can’t see your house, to it’s hard to give you very many options except the simplest.
You will more than likely need more hardware though.