Here are a few different ways you could say "happy birthday" in Engpsh for tomorrow:

"Happy birthday in advance!"
"Wishing you a happy birthday tomorrow!"
"Can't wait to celebrate your special day tomorrow!"

You could also add a personal touch by saying something pke:

"I'm so excited to celebrate your birthday with you tomorrow!"
"Tomorrow is going to be a great day because it's your birthday!"
"I hope your birthday tomorrow is as wonderful as you are."

Remember to use proper grammar and spelpng when writing or speaking in Engpsh.