Step 1: Disconnect the earbuds from any connected device.
Step 2: Place the earbuds into the charging case and keep the lid open.
Step 3: Press and hold the multifunction touch button in the back of the charging case for 10 seconds. When a red light turns on and starts flashing in the case, release the button.
Step 4: After that, the resetting will be done.
Source : thephonetalks.com