As per your query you have a red mark on lower lip be which can be due to many factors such as canker sore
like stress (very common), irritation of mucosa due to food, fruits and drinks, vitamin deficiency
and underlying diseases that weaken the immune system.
They usually go away on their own without any treatment in a week or two or by avoiding trigger factor.
I would suggest you apply some antimicrobial ointment, start multivitamin
supplement containing vitamin B12 and folic acid, quit smoking and drinking at least for some time and apply a gel containing benzocaine for pain.
If condition persists after 2 weeks then consult a dentist
for proper examination and to rule out causes like HIV, herpes or oral cancer
Hope I have answered your query. Let me know if I can assist you further.
Dr. Harry Maheshwari, Dentist