A question which has come up frequently is: Can you fix bad signals?

In short, no.   It is not practical or desirable to do this from an app.

While there are settings which can change wifi radio power hidden in the system settings database on some devices and Android versions, relying on a hack like that would only be permissible if it would provide a benefit which balanced out the power cost.

It doesn’t.  The problem is that the receive antenna, which is what picks up the signal you’re having trouble receiving, doesn’t really benefit that much from more power in proportion to the gain in signal it receives.

You will get far better returns from attacking the problem at the transmission end. Change channels or move your wifi access point into a better physical location if you can.

Typically the more recent a protocol is the more robust it is with noisy environments or low signal.  So, you want 802.11n first, g second, then b/a.

Old routers or firmware will perform more poorly with smartphones and the low-power states their radios go into.  There’s no substitute for updating your wifi access point firmware or buying a new one.