Check the BMW leasing Wiki for info on rules around loaners, incentives etc BMW Leasing Wiki
Go to Edmunds to learning the residual and MF of your car type and deal type
2024 BMW i7 lease Deals, Incentives & Residuals
From there, you can start figuring out how to build your deal and what is required to get to sub-$900 monthly payments. That will just come down to shopping around for dealers to see who will play ball. In my most recent leasing experience with BMW, most dealers were not hyper motivated to give cars away just because they are loaners and if you are leasing, the accident is irrelevant to the cost structure.
In any case, don’t take a unicorn deal like that example as something normal or even achievable for 99% of people. Deals like that come down to right time/right dealer, and some stars aligning to give big rebates and discounts.
edit: I noticed this is a 2023. Go to the equivalent sub thread on Edmunds for the same info