Carlos Queiroz's men are yet to score in Brazil but were hugely impressive in Saturday's 1-0 loss to Argentina, when only a late piece of Lionel Messi magic denied Iran a historic result.
But, having earned a goalless opening-game draw against Nigeria, Iran can still progress and Dejagah believes his side only need slight improvement in Salvador to wrap up the win that could secure their second-round berth.
"Hopefully this third match will bring another step up. We'll definitely be going for goals and we still have a chance to go through, I'm sure of that," the Fulham midfielder told FIFA.com
"What we need to do is take the good things we've done so far, improve a little bit in other areas and give everything to beat Bosnia.
"If we do that - and I think it's a game we can win - we can still qualify."
Dejagah revealed that staying compact had been a key focus for Iran leading into the World Cup, with the side eager to avoid being opened up by some of the world's best.
"We don't have players like Messi, (Sergio) Aguero and (Angel) di Maria, so we need to focus on making ourselves as well-organised as possible," he said.
"The shape of the team, making sure we're tough to get through defensively, is something that has been very important for the coach in the build-up to this tournament.
"He's spent a lot of time on the training field making sure that we have that we're compact and ready to take on the best teams in the world.
"Neither Nigeria nor Argentina had many chances against us and, realistically, that's the only way we can go about things.
"If we played a really open game against players like Messi, they would have killed us."
