The last time the two teams met, the visitors inflicted Barca's heaviest defeat since April 1951 in an 8-2 thrashing in the 2019-20 Champions League quarter-final.
Bayern have won also each of their last 17 openers in the competition since 2003-04, but Barca are unbeaten in their last 22 such fixtures – a run stretching back to 1997-98.
And Koeman is looking forward to the test against Julian Nagelsmann's side as the Catalan club prepare for their first Champions League campaign since 2003-04 without Lionel Messi, who departed for Paris Saint-Germain in August.
"Tomorrow we have the first Champions League game and we are changing things," Koeman told Monday's pre-match news conference.
"Chelsea won last year and was not among the two or three favorites. We know that Bayern is a great team, with individual quality and experienced people.
"We want to compete in the Champions League and we play at home. We will try to get a good result to start the Champions League.
"It's been more than a year and several players suffered a lot in that game [the 8-2 loss]. We have a unique opportunity. We can hurt Bayern and we have a good team. We have to look for our style to hurt the opposition."
Sergio Busquets started in midfield in the crushing defeat, but he is expecting a different challenge with Nagelsmann at the helm.
"They have a new coach and he will try to play his way," Busquets told reporters. "He has kept the entire squad, except for some who have stayed on the road like Thiago.
"He will surely try to win. What happened was difficult to accept, but the world of football is like that. Time has passed and we are psyched that it will be different."
Asked to discuss his team's Champions League hopes following Messi's departure, the midfielder said: "Anything can happen in football. Chelsea won the Champions League and were not favorites.
"The important thing is the collective level and we know that we do not have Leo [Messi] or his individualities.
"We are here, excited and we are aware of the difficulty, but we have a lot of ambition and we want to win."