I had the same question for my Oppo Enco X and I found the answer in Quora. It works!
Below is Amit Kumar's answer:
"Reset the Bluetooth pairing. Place the headphones back in the charging case and keep the lid open. Press and hold the Function button on the charging case until the Indicator blinks. The headphones are now available for pairing with a new device. Then, turn on Bluetooth on the laptop, tap [Search] and select [OPPO Enco W31].
If these fails, factory reset the Enco W31 headphones. With the headphones in the Charging Case and lid open, press and hold the Function button until the Indicator flashes red three times. Then, the headphones have been restored to factory settings. Repeat Step 4 to pair again."