If the watch is paired with other devices , unpair it from the other devices, then re-pair it with your phone. If the original paired device cannot be found, try re-pairing the watch in a relatively less disruptive environment (such as an open outdoor area with fewer people).
If the issue persists, try pairing the watch with a different phone.
For Android :-
Clear app's cache.
(taking iQOOZ3 as an example) :-
Go to Settings > Apps & notifications >See all apps> App info > NoiseFit app > Storage & Cache > Clear cache
Then reset your watch
If the issue still persists , Re-install the Noisefit app, then re-pair the watch with your phone.
Unable to connect phone after disconnection
Check that your watch and the Noisefit app are fully updated.
Turn on Bluetooth and GPS on your phone and grant the Location permission for the NoiseFit app.
Open the NoiseFit app and check to see if your watch can connect automatically.
If the watch can connect automatically, this issue may have occurred because the NoiseFit app is prevented from running in the background. If you are using an Android phone, you need to add the NoiseFit app to the protected list in the background. If you have installed third-party phone manager apps on your phone, add the NoiseFit app to the white list using the apps.
If your watch cannot connect automatically, connect them manually. To do this, open the NoiseFit app, go to Devices, and then go to Pair device.
"If this issue persists, perform the following to troubleshoot:
Disable and enable Bluetooth on your phone and try again.
Restart your phone and reconnect the phone and the watch again.
To reduce the chance that the NoiseFit app is cleared from the background, Lock the App in the background.
Unpair your watch from the phone using the NoiseFit app and then pair them again.
For Android users: Open the NoiseFit app, go to Devices and then select unbind and pair two devices again.
For iOS users: Open the NoiseFit app, go to Devices and then select unbind and pair two devices again. On your phone, go to Settings > Bluetooth, touch the exclamation icon next to the Bluetooth name of the paired watch, and then touch Forget This Device to delete the pairing records for re connection."
Getting "Trying to connect " screen in the app
Disable Battery Optimization in Phone's settings .
For Android users ( taking iQOOZ3 as example ):- Settings > Battery > Battery power consumption management > NoiseFit app > Choose Don’t restrict background power consumption
If the issue still persists ,Force Stop the NoiseFit app.
For Android users ( taking iQOOZ3 as example ):-
Go to settings > Apps & notifications > App info > NoiseFit app > Force Stop
Turn ‘off’ and then ‘on’ the smartphone’s Bluetooth.