Try
Private Sub Command0_Click()
Dim db As Database
Set db = CurrentDb
On Error GoTo Err_Here
DoCmd.SetWarnings False
CurrentDb.Execute SQL
mySQL = "ALTER TABLE [Employees who have matched to Market] ADD [Plug or Match] varchar(5)"
db.Execute mySQL
mySQL = "UPDATE [Employees who have matched to Market] SET [Plug or Match] = ""Matched"""
MsgBox "Flag Applied"
DoCmd.SetWarnings True
db.Execute mySQL
Exit Sub
Err_Here:
MsgBox "XYZ"
End Sub