This is such an interesting question and I am also having a hard time finding this exact reference, but I can help with some context. Slaves in ancient Greece and Rome might have had several sorts of bodily markings, such as scars, branding, or tattoos. In general, scars came from physical abuse and/or the use of shackles; branding was done to shame those captured in war or by certain slaveholders to mark as property; and tattoos could similarly mark property, but were also used as punishment for runaways, so something like a symbol or "catch me" might be tattooed on the face. It can be hard to tell exactly which sort of marks ancient writers are talking about.

Unsurprisingly, slaves would want these marks removed, and we have a lot of literature discussing this from freedmen who wanted the mark of slavery removed. Some covered it, but there is also medical advice for what could be done. There is even the story of one formerly enslaved woman adding her own decorative tattoos to obscure the one that marked her enslavement.

The closest thing I found to the sort of thing you mention is a testimony from Epidaurus that claims the god Asclepius healed a man's mark; he offers a dedication and prayer in thanks. Asclepius was a god of healing, and these sorts of gods were often visited with healing requests. Healing gods were also often used in sacral manumissions, in which slaves were freed at a local temple, with an inscription marking the event. Since these gods were associated with manumission and healing, I think this is the mostly likely sort of temple someone would petition and pray in to have their own mark removed, but again I couldn't find that exact graffiti/inscription. Deborah Kamen has a good overview of slave marks and a more in-depth discussion of the things I mention if you are interested.