Your best method is to contact the seller where you bought them and see how they want you to proceed with repair or replacement. Also just want to ask, is the attached cable in all the way?
Pioneer DJ Team,
I purchased a pair of your HDL-X7-S headphones March 2020. I used them for the first time last week with sound only coming from one side of the headphones. Now they don't work at all? Please send me a new pair and instruct how to return the bad set?