I didn't say that Atalanta has qualified for next season's UEFA Champions League; what I said was that the win Atalanta had against Lecce has given them hope of qualifying for next season's UEFA Champions League because Juventus is leading them by one point and there are two remaining matches for the Serie A season to end. For a long time, Juventus has been struggling to win their matches in the Serie A, which has put them in this condition, and if they continue with such performances, Atalanta might overtake them in the Serie A table. Juventus next match is against Bologna, and they might likely drop points against Bologna, which will give Atalanta an advantage to enter the top four of the Serie A table if they win their match in Serie A.
With Serie A having a share of five clubs that will play in the Champions League next season, Atalanta will certainly play in the competition, because the difference of six points from Roma who are in sixth position is difficult to match, even though Atalanta will probably still be ahead in goal difference, so Atalanta has already qualified for the Champions League and Roma has lost the opportunity to play in the Champions League, so Atalanta's victory over Lecce not only opens up their opportunities but they have indeed got that place.
However, if I judge their performance against Lecce, it was not an impressive performance so I doubt they will be a competitive team in the Champions League unless they make some changes to their squad.
Of course, Atalanta will try to make the right transfers to build a squad ready for the Champions League next year, but it is not right to say that this year was unsuccessful for them. They reached the final of the European league and maybe they will win the cup. Their chances against Bayer Leverkusen are quite low, but we know there is still a possibility. They might even have a chance to get out of the group in the Champions League with the current squad. However, I am sure that they will try to build a quality squad with players who will definitely be added to this squad. Since they are among the top 5 in the league, they will go to the UCL next year. I think it has been a successful year for Atalanta.