Milan is just a bad team in the first place, they have Gimenez, Felix and Walker, their performance aren't that bad actually, they can still perform. Bologna's squad is a combination of young players who not able to reach senior team, second tier players and old players who no longer playing in senior team, yet Milan still lose.
Better to sack the manager instead, maybe Italian teams good when they get managed by Italian managers too. Inter, Atalanta, Napoli, and Juventus are managed by Italian managers. Milan was better when Stefano Pioli was the manager.
Despite having a better team, AC Milan is unable to win games. Their lack of goals and defense's failure to stop opponents from scoring goals caused them to be eliminated from the Champions League, and even though they have strong attackers in their front line, they are unable to turn many opportunities into goals. Milan was leading Bologna with a goal in the first half but lost the game after conceding two goals in the second half.
However, firing the manager is the best option for AC Milan, otherwise, they risk ending up in a position where they are not expected this season. If Milan had won the game against Bologna, they would right now be in eighth place in the table, 5 points behind 4th place. Sergio Conceicao can follow Paulo Fonseca since he refused to play with Chukweze, however; I believe he is underestimating the player because he has only played 40 minutes in the previous four games and was even on the bench against Bologna, and Conceicao was unable to bring him in during the match.