This is the Secret dialer code launching option. A dialer coder is a series of digits prefixed by
*#*# and followed by
#*#* that you enter into your phone dialer and which can trigger a certain action or, in this case, launch a cloned app.
Unfortunately this isn’t supported by all devices. For example, it doesn’t work on Samsung devices. This option only makes sense if you also remove the app’s launcher icon, so that the cloned app can only be launched via the secret dialer code.