Can you say a little more about what the app says while you are trying to get the robot to connect? Which steps seem to work and which don't? Do you see an error message in the app?
Also, try restarting the robot. Hold down the play button for like 8 sec until the robot's power level indicator (the bar of LEDs nearest the dustbin button) pulses inwardly and then goes out. After that, lift the robot out of the charger and place it back there to restart it.