Step1: Reboot ASA
Step 2: Wait till the you can see following “Use BREAK or ESC to interrupt boot.” and then hit the ESC key, works on MAC/Terminal as well. (see below)
Step 3: Then you should land in “rommon #0>”
Step 4: Change the confreg valu to 0x41 as it tells to ignore its saved (startup) configuration upon boot
rommon #2> confreg 0×41
Step 5: reboot
rommon #2> reboot
Step 6: After the reboot you need to change the confreg value back to 0x01 and reboot.
ciscoasa(config)# config-register 0x01
ciscoasa# reboot