The method varies with the TV. You have not provided enough information.
Details of how to do this will be in the manual. If you do not have a copy of the manual then you need to find out what the make and model number of the TV is and locate a manual on-line for that model.
Withheld
July 2012
Automatic Answer
We may have found other answers which could help you.
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix dtt receivers.