A classic case of poor naming convention

We have used the name “GO” twice

1st “we create a stored procedure “GO”

lets change its name to “My_Proc_GO”.

2nd we use the batch...

You can use the monthname function then just take the left 3 characters

=Left(MonthName(Fields!MonthField.Value),3)

You might consider rotating the text as well

The word "button" implies you want more of your own web site. SSRS does not allow the addition of buttons it is simply not in the tool bar.

If you want...