Assigning VBA Code To Command Button?

I have placed a CommandButton1 and CommandButton2 on the Sheet1....how do i then assign the macro code to these Buttons

CommandButton1 is called MANAGERS GROUPS (macro called Split Sheets)
CommandButton2 is called CLEAR MANAGERS GROUPS (macro called clear_managers)

It was working before as i just used rectangle shapes as the buttons but have since removed these shapes and used the CommandButtons

The error is below in RED

Code:
Option Explicit
Public TrainingRows
Sub SplitSheets()
'
Dim rCell As Range
Dim sht As Worksheet
Dim lastrow As Integer

[code].....