How to treat cold sores?

My 15 month old woke up yesterday morning with a cold sore on her bottom lip line. She has a appt with her doctor Monday. Is there anything I can put on it until then? It doesn’t seem to be bothering her at all. I just don’t want it to get worse. I’ve just never heard of a baby as young as he getting one. She does have a runny nose but that just started this morning.