value of a cell into a text box

Which cell contains the value? You can simply use the UserForm_Initialize event to populate a TextBox

Private Sub UserForm_Initialize()
Me.TextBox1.Value = Sheet1.Cells(1, 1).Value
End Sub

You aren't using formulas in a userform. Do you mean a VBA userform?

I think this is what you want

Private Sub UserForm_Initialize()
Me.TextBox1.Value = Sheet("CORRECT FORMAT").Range("AO7").Value
End Sub