You'll need an advanced action that takes the value entered in the text entry box (TEB) and jumps to the desired slide.
TEBs are associated automatically with variables that are assigned when you create the TEB. The advanced action is associated with the TEB and is triggered by clicking the SUBMIT button that appears automatically. Be careful, though: the command to go to a slide numbers all slides starting with zero, so you first have to subtract 1 from the number the user enters.
So, if your TEB variable is something like TEB_1 (or whatever you change it to when you create the TEB), the advanced action would read:
Decrement TEB_1 by 1
Assign cpCmndGotoSlide with TEB_1