My preferred approach is to recast that project as “Current Sprint.”
One time, archive the previous sprints’ tasks to either a) their own individual archived projects, or b) one archived project with sections for each past sprint. First make the project(s) and sections you need, then multi-select each sprint’s tasks, sprint-by-sprint, and use the bottom multi-select toolbar to add them to the desired project (and optionally section) and then remove from the Current Sprint project. Finally, remove the empty past sprint sections from Current Sprint.
Going forward, at the end or each sprint, do the above for the just-completed sprint, but you won’t have sections anymore, just multi-select all completed tasks for archiving.
Hope that helps,
Larry