Your question is a little vague so I am not sure exactly what your requesting. Perhaps if you could expand or provide some more detail I can best answer your question.
Items that have been recorded stay in your listing until deleted. (unless using a series manager set to bump old recordings off when the DVR gets full automatically)
If you are referring to the recently watched On-Demand history that is set to 24 hours and can not be modified.
Assuming you now have room, show didn't get overwritten and you have version 1.9 (everyone does except northeast) do the following:
Bring up DVR menu. Go to recent deletes. If the show you are looking for is listed, scroll down to it. Select ok, Select restore.
Should be good to go. If not listed, that means it was overwritten on HD so no way to get it back.