Pokemon-go – Pokemon GO Login

I have a question about signing in to Pokemon GO. My phone is signed in with another email that I use. But when I first opened the app (after I clicked the sign in with gmail button) , it signed in with the email that was on my phone.I wanted to use another email on the game because originally I started the game on another phone with that other email. How do I make it that I use the other email that I wanted to use because by default the game is using the email on my phone!( I am using a galaxy phone with google play if this information helps ) Please help!