Usually, doubling may be caused by the following reasons: IPD is not well adjusted; the phone is not centered, or the glasses do not support your IPR range. You can adjust according to the glasses instructions.
If you still cannot solve the problem, we would need more information to help. If you would, please oblige us to take a screenshot of your video playing screen, when it's in left-right mode (VR mode). Please also send us the name of the video with the brand name and version of your mobile phone; we would also like to know the brand and make of your VR headset.