If you want to do this in code, use a code step similar to the following:
Me.txtBoxName.DefaultValue = """" & _
InputBox("Enter the starting value for txtBoxName:") & _
""""
Or, you can use an expression similar to this in the Default Value property
of the text box (open form in design view, click on the textbox control,
open the Properties window, click on Data tab, and click in the Default
Value box):
=InputBox("Enter the starting value for txtBoxName:")