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.
However, that is likely to be no easy feat versus a Real team that, like Bayern, has only suffered one defeat in the competition this season.
And Guardiola knows the Bavarians will need to produce more going forward in order to seal progression to the tournament showpiece at Estadio da Luz in Lisbon on May 24.
"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."
Guardiola is wary of the threat posed by Real, who are expected to have their attacking trio of Karim Benzema, Cristiano Ronaldo and Gareth Bale available to feature.
Bale is poised to return after missing the 4-0 win over Osasuna through illness, but Guardiola is not concerned by the presence of the Wales winger, and is hopeful that the support of the home fans will see them through to the final.
"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."
