You will need to make a userForm with the three textboxes on it. (and a label
telling the user  what to do). Also include two buttons one for OK and one for
cancel.

Declare (Dim) the three variables outside the sub so they are available to
both the sub and the form

In the sub put Userform1.show

In the form code  for the OK button put code to set each of the three variables
equal to the textboxes on the form
Then put

Unload me

Also put unload me in the sub for the cancel button (you might need to put
some more code to handle errors, cancellation etc)