The Gunners centre-back says the team must go back to basics on the training ground after the second leg defeat to Barcelona on Wednesday night.
A resilient and encouraging performance was not enough for the Gunners as they lost 3-1 to the Spanish giants at the Nou Camp in their Champions League last-16 second leg on Wednesday night.
That defeat saw Arsene Wenger's side exit the competition at the first knockout round for the sixth season in a row and leaves their season on the verge of being over, with the club out of the FA Cup and 11 points off the pace in the Premier League.
Koscielny,who has played 34 times in all competitions for the club this season, says that they must start getting things right again soon if they are to revive any chance of winning the title.
The 30-year-old told the club's official website: "We haven’t been fighting like we did in the last six months because we lost a little confidence in ourselves and it is harder to win some games.
"We need to come back and help our team-mates with defending, attacking and a controlled passing movement. We didn’t lose our capacity physically or our technique, we just need to do more.
"We also need to come back to our basics, be simple and then the confidence will come back. When we get a win, it will be better and after we can play with more confidence, movement and try things we didn’t do before. We need to get back to this and when the results come back, we will be stronger."
With only the league left to focus on, Arsenal travel to Goodison Park to take on Everton this weekend and attempt to close the gap on rivals Tottenham Hotspur and leaders Leicester City.
If the Gunners fail to make up the ground and win an increasingly-unlikely league title this season, it will be a first campaign without a trophy in three years after back-to-back FA Cup successes.
Wenger's side have not won the Premier League since the 'Invincibles' season of 2003-04, when they went all 38 league games without defeat,