You can’t send items back as lessons, but you can pinpoint groups to learn at a time with the Reorder script. Pinpoint one set of reviews, say, Level 10 Kanji only, and spend the time relearning. You can come back to this group repeatedly without being overloaded with all the other reviews in the queue. Then as you become comfortable with them, isolate level 10 vocab or level 11 kanji, and work on them until comfortable, while also keeping up the level 10 kanji. Add in what you are comfortable with until your backlog is gone and you’re ready for new lessons, whether than takes a few days or several weeks.