It would be very unusual to destroy the bootloader accidentally, there’s no way to overwrite it easily from firmware.
Anyway, to connect the ST-Link you might have a look the OWL1 pinout that has SWD pins at the same location as OWL2 used on Lich. You need to connect the pins labeled NRST, SWDIO, GND, SWCLK, +3V3 to the same pins on your debug probe.
You should connect the USB VBUS pin to a +5v pin with a jumper cable, and power it with USB Micro. I can send you the exact openocd command if you manage to install and run that software. Alternatively, there’s also some GUI utility from ST for flashing that you could use instead, but I’m not too familiar with it.