How to give small dent on a body

[Anonymous]

(English is not my first language so I'm sorry if it's a bit confusing)

My design

I want to create a little dent along the lips to create a mouth/smile line and i couldn't figure out how. My last resort would be get them printed and give the mouth line manually using mini grinder lol

[etfrench]

Sweep would be the tool for this.  Draw the profile of the dip, then use the edge of the lips as the path in the Sweep tool.