If you have to ask, you'll probably cause more problems when you try, then you'll have to pay someone to fix those problems before they can fix the problem you have now (which you'll have to pay for) - so it's usually cheaper to just bring it in to have it fixed.
You have to open the tab to make sure that the touch screen cable didn't break at a connection point, or a connector got dislodged. If there are no problems there, you have to hope it's just a damaged touch screen and replace it. If some silicon controlling the touch screen got damaged you have to replace the whole board, and by that time you've spent as much as replacing the tablet. A shop will throw in a scrap touch screen first, to see if it's the screen that's bad. If not, they'll stop there so you don't pay for a new screen you can't use anyway.