What's been left out: you should contact Lenovo support and ask them to instruct you in order to downgrade your bios. You need to know what version you came from, though (what version it was shipped with and lived on when bitlocker was already active). That may not even be possible to downgrade since some bios' do not allow it, but Lenovo will know this. After downgrading, windows will start without the Recovery key being asked for.
Things to learn: have a backup.