It depends on what type of buttons you have.
If you have a Form Control button then right-click on the button and select "Assign Macro". You should see a box at the top that says "Macro Name". In that box you should see something that looks like this "Book1!Sheet1.Test2Button". The portion Book1 just tells you the name of the workbook (Excel file) that the macro is in. !Sheet1 tells you that the macro is in the sheet module for the sheet named Sheet1. Your button may not have that portion if the macro is in a standard module. The actual name of the sub that runs when the button is select is Test2Button. You can pull up the VBA editor using Arlette's instructions above and do a search for that macro name to find it.
If you have an ActiveX control button instead the easiest way to find the code is to enter Design Mode. You can find this under the developer tab at the top of the screen. If you don't see the Developer tab you need to activate it by going to File --> Options --> Customize Ribbon and then checking the box in the right window next to Developer. Once in Design Mode, simply double-click on the button. The VBA editor should pop up and you should be in a sub that looks something like this:
Private Sub CommandButton1_Click()
End Sub
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