Haaland scored both goals in the second half of the 2-0 victory at the Etihad Stadium on Saturday, but afterwards Guardiola said the Norwegian's body language during the first 45 minutes was "not good."
City resume their UEFA Champions League defence against Copenhagen on Tuesday and ahead of the game, Haaland, who has returned after two months out with a foot injury, has been told by his manager to stay positive, even when he's not scoring.
"Erling is young, playing in the most difficult position on the pitch surrounded by four or five players with minor space," Guardiola told a news conference on Monday. "In the first half [against Everton] maybe we didn't have the special delivery players, like Kevin [De Bruyne] for example, who can find him. In that moment he has to be positive. It will come.
"When he scored a goal, he reacted but he doesn't need to score because he helps us for many things. Not just score a goal.
"Back [after two months out] is not easy and he's a huge competitor who wants to score goals. Ok, I know that, we know that, so relax."
City head into the round of 16 of the Champions League as one of only two teams to win all six group stage games along with Real Madrid.
Guardiola's team are bidding to become the first side since Real Madrid's three-peat in 2016, 2017 and 2018 to retain the trophy, and the 53-year-old says belief in the squad is higher after being crowned champions of Europe last season.
"When I arrived eight years ago I had the feeling maybe this competition was too much for us," said Guardiola. "Our defeats and bad moments helped us to grow up and being in the position we are -- two finals and one semifinal in the last three years -- the whole club has awareness that we can try to be ourselves.
"Before, I felt they were saying 'are you sure Pep? Are we ready to do it?'
"Now the whole organisation believes we can do it."
United were beaten 4-3 at Parken Stadium and Bayern fell behind before narrowly winning 2-1.
Copenhagen haven't played a competitive game since their final group game against Galatasaray on Dec. 12 because of Denmark's winter break but City defender Nathan Aké is still expecting a difficult night.
"We know it'll be tough," said Aké. "The group they were in was one of the toughest and to come out of that shows what a top test we'll have. We won it last year but it doesn't change the fact that we want to do the same and go as far as possible. It's probably one of the hardest competitions in the world."