Did you connect your watch to the bluetooth of your smartphone directly?
Please do not pair the watch directly with the Bluetooth in your mobile phone's settings. This will not allow the watch to get paired through the App. If you did paired your watch with your smartphone, please go to settings of your smartphone and select "forget device"
Then, you can go to the App just with your Bluetooth of your smartphone ON, and with your watch nearby, and select "device" " and then the + sign and bind device"