Use APKPure App
Get WiFi AP Manager old version APK for Android
WiFi Access Point Manager für Android
This app will help you to control your AP. With this app you can do whatever AOSP's settings allow plus you can see connected devices and block unwanted devices by their MAC address(but you need ROOT access for that). This app is open source so you can do whatever you want with it's source code - https://github.com/sssemil/WiFiAPManager (it's published under the Apache License Version 2.0).