Thats a really easy fix.
First you have to determine which colour of black you have.
Then order one of these:
https://www.ebay.co.uk/itm/BMW-Dakota-Black-N6SW-Leather-Touch-Up-Pen-Colour-Repair-for-Car-Seats-/261230385714?mkcid=16&mkevt=1&_trksid=p2349624.m46890.l49286&mkrid=710-127635-2958-0
I apply with a damp microfibre cloth, helps spread the dye.
You may want to give it a good clean first, with pampers wipes and dry it fully before you use the dye.