Casio G-Shock Database

Subseries:

GMW-B5000
Press and Hold "A" until "HT" blinks (about 10s). Press "C" 2 times. Press and Hold "B" until "Pair Clear" is displayed and the watch beeps once (about 7s). Release "B" immediately after the first beep. If you do not release "B", a full reset is performed. "Reset All" is displayed and the watch beeps again.

For most models, deleting the bluetooth pairing is explained in the manual. For some models, there is no info in the manual.

Why deleting the bluetooth pairing?
There is a known problem with displaying the sucessful time sync in the watch display. Normaly the watch displays "RCVD" when time sync (bluetooth or MultiBand) was sucessful.
MultiBand time sync is usually between midnight and 5am. Bluetooth time sync is 4 times a day, at: 0:30am, 6:30am, 0:30pm, 6:30pm.

If you delete the pairing only on your smartphone, because you just wanted to use the smartphone app for the initial setup and want the watch to use MultiBand time sync on a daily basis, the following is happening.

If the watch sucessfully receives a time signal via Multiband between midnight an 5am, "RCVD" is displayed. At 6:30am the watch tries to perform a time sync via bluetooth. This will fail (because pairing on the smartphone was deleted). As a result the watch will remove "RCVD" from the watch display to indicate the failed bluetooth time sync. If you're going to check your watch after 6:30am, no "RCVD" is displayed, even if time sync via MultiBand was successful. This means, you don't know if the watch is on correct time. Unless you check after MultiBand time sync but before 6:30am.

By deleteting the pairing information on the watch itself, you prevent the watch to do a bluetooth time sync attempt. Therefore "RCVD" is displayed, if the MultiBand time sync was successful.

Also, deleting the paring information will help to keep your battery charged!