There is no sure way to uninstall a hidden spy phone app on Android. The best way to try and remove it would be to factory reset the device, but this may not always work.
What Do Spyware Apps Look Like On Android?

Spyware apps can look like any other app on your Android device, but may exhibit some unusual behavior. For example, a spyware app may send unexpected or excessive text messages, track your location without your permission, or use your device to send spam.
If you suspect that an app might be spyware, uninstall it and then run a virus scan on your device.
Can You Tell If Your Cell Phone Is Being Tracked?
There is no sure way to tell if your cell phone is being tracked, but there are some signs that may indicate that it is. These include unexpected increases in data usage, unexpected changes in the phone’s location, and unusual activity on the phone itself.
What Happens If You Dial *# 21?

This is the code for “Call Forwarding When Unanswered.”
“Call Forwarding” allows you to forward your mobile device’s calls to another phone number.
What Is Hidden Menu App?
A hidden menu app is an app that allows you to access hidden menus on your phone. These menus may include options for customizing your phone or for troubleshooting problems.
Will A Factory Reset Get Rid Of Spyware?

A factory reset will remove all files and settings from your device, including any spyware that may be present.
If you are unsure whether your device is infected with spyware, we recommend running a malware scan before performing a factory reset.
Can You Tell If Your Cell Phone Is Being Tracked?
There is no sure way to tell if your cell phone is being tracked, but there are some signs that may indicate that your activity is being monitored. If you notice that your battery life is suddenly shorter than usual, or if you notice strange activity on your phone bill, these could be signs that your cell phone is being tracked.
What Is The Use Of * * 4636 * *?
This code can be used to open the Test Menu on your Android phone.
The Test Menu gives you access to various diagnostic tools that can be used to test the various hardware and software components on your phone.
You can use the Test Menu to test things like the display, speakers, camera, sensors, etc.
What Happens If You Dial *# 21?
This is the code for “Call Forwarding When Unanswered.”
“Call Forwarding” allows you to forward your incoming calls to another phone number.
“When Unanswered” means that the forwarded phone will only receive the call if you do not answer your phone.
Does Spyware Work If Phone Is Off?
No, spyware only works when the phone is on.
If you turn off your phone, the spyware will not be able to track your location or collect any data from your phone.
Can Spyware Stay On Your Phone After Factory Reset?
Yes, it is possible for spyware to remain on your phone even after you have factory reset it. If you are concerned that there may be spyware on your device, you can install an anti-spyware app to scan for and remove any malicious software.