by opening your mouth and saying it
don't hurry up.. let her understand it.. do things so that she can feel it.
If you don't know how to say it, you might not want to say it.
Are you sure you going to feel it again tomorrow?
"Oh hey, I love you."
Get your mouth out of the chicken butt and say I love you.
Just straight up say it. Unless you barely know the girl then you need to talk to her more and work your way into telling her.