This is a retro design to confront teams with actions from retros that have not been put into practice. Without actions there is little point in the retro, right? This is not a format you can run regularly - ideally you should not have to!
Start of by hunting down all the outcomes from the previous 4-5 sprints. Print them off in large print, cut into individual cards, fold them up and place them in a bowl. On a board or wall, draw out 3 columns - Ditch, More and Done. The team now take it in turns to pick an action from the bowl and place it in the column they think the action is relevant to.
Encourage discussion at this point - I played devils advocate often e.g. "I thought that was done?", "Didn't you do that?", "Yeah, we said that 3 months ago...." - you might not be so mean.
If actions are in More they are still relevant so there is no reason why they should not be done. Anything in More represents a missed opportunity for change. It is worth pointing out how awesome these ideas are and that they already came up with them - seems like a bit of waste.
Ditch suggests this is no longer relevant - you might want to explore if this is because they are old or we have evolved as a team. You might want to ask why didn't we need it? What do we know now that we did not know when we came up with this action? How did we ever survive without it?
You can also look at the Done actions and look at why they were Done - are they special/easy... what was different? It might come as a surprise how little has been 'Done'. This can be a valuable learning exercise in itself.
You can now focus the learning on why we did not do these things and then tease out which ones from More should we do immediately. Make sure the team buy into addressing these items in the next sprint. Ask the question "What could we put into practice today?".