If you kiss someone who has a cold sore on their lip then you're likely to get infected with the virus that causes the cold sore.
If you do kiss someone who has a cold sore then there's not much you can do other than wait until you get the cold sore and then apply some Aloe Vera Gel to the cold sore which will help it heal and go away.
You can also dip a Q Tip in some salt water or water and baking soda and apply the salt or baking soda to the cold sore or apply some ice to help with the cold sore.