The Pulse device may be sleeping - wake the Pulse device by pushing the measurement button on the device.
Check that the unit battery still has life. Push the measurement button on the Pulse (again). This will tell you the battery is fine because you will see the measurement lights flash and second it will refresh the Bluetooth communications, so check the list again.
Lastly turn off the Bluetooth on your phone then remove the battery from the Pulse for a few seconds. Put the battery back into the pulse, wait for it to boot up (the measurement lights will stop flashing) then turn the Bluetooth back on your phone. This will have fully reset the Pulse and you should see it on the “Select Device” list.