I recently did a 1200+ review pile, and this is my recommendation:
Don’t reset. Don’t worry about what’s in apprentice, guru, etc. Don’t worry about your accuracy.
Do daily review sessions in 2 groupings of 50 reviews per group, so that you’re clearing through 100 reviews per day. You will get through this, guaranteed. Your accuracy rate will come back up again, guaranteed.
Know that you will have waves of “completely unfamiliar” kanji that will knock your accuracy back down, but that you will relearn each wave relatively quickly due to your prior exposure. Having large numbers of kanji back in apprentice is not a problem. This just means you get to have abundant exposures, which results in solid relearns over time. You won’t regret this.
I am super super glad I didn’t decide to reset. It would have been a waste.
The important thing is to know that you can do this, and know that the “low scores” you see are actually big wins for your recovery because you are “unlocking” the old kanji into learner mode again by bringing them back down into apprentice! There’s no reason to add kanji to that stack that you already know, and if you reset to older levels, you will be doing exactly that. You will not be saving time. You will not be saving labor.
I feel you on the low accuracy. My accuracy was at 40% when I started chipping at my queue, and it dipped even lower several times as additional waves of “enlightened” items were unfamiliar to me. But I kept at the 100/day (Trunklayer’s advice) and when I was noticing that certain ones were staying down and not getting learned, then I would look carefully at the mnemonics again and try very hard to pay very close attention and before I knew it they were learned and I was getting better scores. My highest scores were in the low to mid 70% accuracy on old items, increasing to 80s when I was just burning and hardly had any enlightened unfamiliars. Then a new wave would knock that back into the 20-30% range. That didn’t really improve until the end, but when it did, when my accuracy was getting up into the high 80s and low 90s I knew I was very close to closing the queue!
You can do this. You don’t need to reset – just keep reminding yourself: low accuracy is a win for each of those kanji that you don’t know because you’re going to get the chance to relearn them through exposure.
I wish you the best with this! Don’t give up!