Guardiola's men trail 1-0 from the first leg of their semi-final tie at the Bernabeu, a game in which the holders were not at their free-flowing best in attack.
Bayern will aim to turn that deficit around in Tuesday's second leg at the Allianz Arena and keep their quest to win five trophies in a season intact.
"We're 1-0 down, but nothing's decided yet," Guardiola said. "We'll need to score two or three goals though.
"We need to be more threatening in the return leg. I haven't decided yet what changed I will make."
"To me it makes no difference whether Real have Cristiano Ronaldo and Gareth Bale available," Guardiola added.
"I can't imagine Real's approach will be all about defending their result. Real have quick players which makes them very dangerous opponents.
"We can't do it alone. I'm confident that the fans will be behind us tomorrow (Tuesday).
"But at the end of the day, it's down to us. The fans can't score a goal."
