I think it depends a lot on the context. One word is 'roll'. We can talk about 'rolling dough into a ball', it is used when talking about making something into a sphere shape. The word 'roll' actually has a lot of meanings. We can also say 'curl'. I have a feeling this is not the meaning you mean though. When you make something into a partially rounded shape we use curl, like curling your hair. The adjective round can also be used as a verb. You can say 'I rounded off the edges of the cake with a knife' Can you give a more specific example of a sentence and I can suggest the most appropriate word?

With lips, you can use the verb "to purse" if you mean to bring them together e.g. ready to kiss someone, or when you are feeling dubious about something. Otherwise, we generally use the expression "make sth round".