For the ESP-01 to successfully act as a Wi-Fi modem for the Arduino, it has to be running the factory ‘AT’ firmware.
You’ve overwritten this firmware with your WifiManager sketch, so to get it working again you’ll need to download a new copy of the factory firmware and upload it. I don’t think this can be done with the Arduino IDE, but a bit of googling should show you how.
WiFiManager doesn’t work with the ESP-01/Arduino combination.
Also, WiFiManager won’t solve connectivity problems, it’s a method of allowing you to enter different Wi-Fi credentials without having to re-flash the device with new code that has hard-coded credentials.
Your connection issues are probably caused by badly written code.
If you’re new to IOT you might find it easier to start with a different type of board, especially if you do have a need for WiFiManager…
Pete.