Here is an example how a retrospective can be done:
The project manager organizes it. Invite the entire team and the Product Owner, optionally other stakeholders if useful and they are interested.
Ask every team member to write down on a post-it note (short, concise) what went well in this just finished iteration and what can be made better in the last iteration.
Use different colours for the two.
Put them in different columns, as “the TEAM can improve it”, “the ORGANIZATION must improve it”.
The improvements in the first group (team) are then further discussed and responsibilities are shared and the needed actions are going into the product backlog, ideally all into the next sprint backlog.
In any case they get a priority.
The items belonging to the second group (organization) are going into the impediments log as actions which the project manager will raise and solve in the next sprint.
Do not try to handle all of them (especially in the first retrospective the team members will come out with a lot of suggestions): select a few of them, by what is rated most important by the team (for example, members can get stickers to attach next to the suggestions they prefer: the top 3 or 5 suggestions get chosen).