I have three reading,

I have to insert first reading first (text1.text) , After I save the first reading for first records, I want it pop up the messagebox, You want to add records for reading two? Text1.text = text1.text + 1, If I click yes, now text1 show me number 2 that mean it increase to 2 from first reading. I am no idea to start it. How to do that?