Detailing supplies for scion xd

i had my 2008 scion xd detailed last year and they said they used this black dye on the cloth seats which made them look like new. the guy who worked on my car said i could do it myself- just need to buy the dye. where do i buy this…what kind…how to apply? is this something i shouldn’t do myself (don’t want to ruin the seats; i have a black interior- seats are black with subtle blue pattern on them)?