The Terriers haven't won a league match since December 16 and have fallen into the relegation zone.
But the German insists he has done everything to help his players think positive.
"Don't start to overthink situations and don't start to panic or lose your calmness," Wagner said.
"We have to show exactly what we like to do and what we have to do."
Town travel to Birmingham on Tuesday after they drew the first tie 1-1 at John Smith's Stadium.