Barca are in Madrid for the second-leg of their Champions League quarterfinal needing to overturn a 2-0 deficit.
Flick said: "We need to focus on putting on a good performance and not so much on the result, because when we play well we are capable of scoring goals.
"I have a feeling it will be different from the first leg. It will be incredible. We can come back. It's possible. We know we're playing against a strong Atlético side, with good attacking and defensive players. We have to be strong in every aspect and take advantage of our opportunities."
"Mentality and attitude are very important. My team, as I've already said, needs to be connected with the fans. And we see the respect they have for our performance.
"Every action will be important. We have to believe. The team is on the right track. We have to be brave and play well. We have quality. In matches against Atlético, we're usually a better team."
On Lamine Yamal's form, Flick added: "I think Lamine has performed very well. I'm very happy with him. He needs to do what he does best, one-on-one situations... we need to have different options... We have to play as a team.
"That's the most important thing. I don't care about individual performance. The team is the most important thing. Games can be decided in a single moment. Let's hope it goes our way."