Adding a value textbox to a userform

Hi Forum
Wonder if anyone could help me adding a textbox to a userform that will show the highest current number in Row A,
I can add the textbox ok and can create a formula to show the highest number but not getting anything to show on the userform textbox. The Private Sub I created is as below so looking for a formula that will make it pick up the amount sitting in Row AM1 of worksheet2

Private Sub TextBox1_Change()

End Sub

Thanks for any help you can provide.
J