All right! Everything's done. I think the code can be more simple for my game, like this
Option Explicit

Sub IncreaseScore()
Dim i As Long
i = CLng(Slide1.Shapes("TextBox 7").TextFrame.TextRange.Text)
Slide1.Shapes("TextBox 7").TextFrame.TextRange.Text = Format(i + 1, "#,##0")


End Sub


Sub abc()
Dim a As String
a = Slide1.Shapes("TextBox 9").TextFrame.TextRange.Text
Slide1.Shapes("TextBox 5").TextFrame.TextRange.Text = a
End Sub
But there's still a problem. a can't get text from other slide, such as Slide2, I use a = Slide2.Shapes("TextBox 3").TextFrame.TextRange.Text on Slide1 (code) window, the error is "variable not defined". So how can I get textbox from other slides?