You can't replace the screen, so you may have to try resetting the device. You can simply hold the reset pinhole using a needle or a toothpick for 10 seconds. If that doesn't work then you can try going into the Recovery System and selecting the Force Touchscreen Calibration. You can get into the recovery screen by
-Turn off the tablet and wait 10 seconds.
-Press and hold the volume + button while powering on the tablet.
-Keep the volume + pressed until the Recovery Mode has started (White Screen).
-To move from option to option, use the volume buttons and press the ON/OFF button to select the option.
After that select the touchscreen calibration and follow the instructions. That should fix all the issues you are having.