I’ve done that myself a few times and it’s such a pain, I really feel for you! I do 5 vocab a day and usually prefer to go at a pretty steady pace, so having so many reviews at a time really is daunting. I’m not sure if anyone else has a better way of doing it, but I tend to break it down into chunks and set myself a daily goal to gradually whittle them down.
I recently took a break and forgot to put myself on vacation mode and came back to about 400 reviews, so I timed myself to see how long it took to get through 10 reviews so I could work out how long it’d take me to review everything. On average it took about 4 minutes to review 10 at the start while my memory was a bit rusty, but once I got back into the swing of it after a few days, it generally took about 2 minutes or so to get through 10 reviews. Let’s take an average and say it takes 3 mins to get through 10 reviews.
Depending on how much time you have to do them, your mileage may vary. But I tend to attempt to do about 50 or 100 reviews a day in a situation like this depending on how busy I am. 50 a day, split into two batches of 25 in a morning and evening will take about 7.5 minutes a session, or about 15 minutes a day in total and will mean it’s down to zero in 24 days. Or if you have more time, 100 a day split into managable chunks of four lots of 25 will take you about 30 minutes a day in total and will mean that it’s down to zero in 12 days- less than two weeks!
I hope you manage to get down them and back to a comfortable zero soon! And I hope you had a nice relaxing break, too. Good luck!