Seller has swapped my label by accident so i have received the wrong package

Uh so i bought some p6000 of a seller and he accidentally swapped my label with another package so i received some boots instead of the p6000 the other buyer has already shipped the shoes i bought back to the seller but i still have the sellers other package and basically vinted told me to return it but i need a qr code from the seller but he dosent know how to get one and i dont know how to track his package when i send it and the guy said he will pay for my return by discounting the original item but i dont know how to return i went to my local shop and gave them the shipping adress but they said they need a qr code from vinted