Same thing happened to me last night. Updated BIOS through Legion Space and it went to black screen. it took me a couple hours but here's how I did it. I downloaded a different BIOS from March, then hooked the Go up via external display. Navigated the BIOS menu with FPS mode and controllers connected. It's a pain but I was able to get into BIOS and enable the BIOS Flashback. Then I pushed the new BIOS file through and it worked. Hardest part was getting the BIOS menu to work with FPS mode. I tried external mouse/keyboard with no success. FPS mode was the only way.