Ferran Torres and Lamine Yamal struck for Barca in Belgium.
Afterwards, Flick said: "3-3 is not the best result, but Club Brugge played very, very well.
"We will continue to maintain our high defensive line and work on improving it.
"Last season, we wouldn’t have conceded that first goal. We don’t have the same confidence when playing the offside trap. We won’t change our way of defending.
"In midfield, we didn’t press well, and it was difficult to defend against their players with pace. We need to analyse the draw and see where we can improve."
The German added, "We have to keep working. We are not at our best, but we must stay positive. We’ll be able to get back to our best level when we have the likes Raphinha, Pedri, and Joan Garcia back.
"We are Barça and we want to be intense with and without the ball.
"We can change some things, but we also have to stick to our philosophy. We don't have to change our style of play; we are Barça. This isn't about the philosophy. We can do things better.
"When there's no intensity, we don't have chances. Teams in the Champions League make very quick transitions, and Club Brugge did that very well, and we respect that. A 3-3 draw isn't a good result, but we came from behind."