Learning / studying is pretty subjective I think, so it’s hard to give general advice.
I’ll just blabber on about my personal experience, see this chart for my qualifications 
Resetting to level 1, or even just to five levels or more below me, would discourage me a lot.
Because even if there are a lot of items you don’t recall right away, there is a pretty good chance you will be able to re-learn them quicker than a reset would allow you.
I came back to a ridiculous amount of reviews and tried tackling them head on over a long period of time. At some point I realised that given my 1500+ reviews, WaniKani’s very randomized review mode was making it really hard for me to get anywhere.
The reorder script solved that problem entirely, by allowing me to a) sort by SRS, making sure I’d see items again soon after failing them and b) to sort by type, giving me a motivation boost by being able to specifically review kanji from time to time. Normally they were coming up very rarely, burried beneath literally hundreds of vocabulary items.
Big shout out to @Kumirei : Thank you so much, your Reorder Omega really saved me a lot of time and stress.
I was also careful to not over- or under-do it. Doing all the reviews in one go would have taken me literally the whole day with how much I had forgotten, and it would probably have burned me out for a few days at least. But more importantly, it would obviously have meant that the items would have come back in large chunks of over a thousand next time.
So I set a goal to a) preferrably do a hundred reviews each day and b) not to let the total number of reviews avaibable fall beneath the count on the day prior (in steps of a hundred). So if I reached 1400 reviews on my pile, I wouldn’t let it get over 1400 again at the end of the following day. (Due to work, university and personal issues I didn’t manage to keep that up all the way through, but as a general guide line, it served me well).
There are a lot of “speed demons” here, which can make this feel like even more of a set back. Don’t let that discourage you. The important thing when learning anything is not to stop and to just keep making progress however small it feels. It does absolutely get easier again. Otherwise I would not even have the time to post this long *** reply.
