You can see the stored firmware versions in CLISH:
> show diag
Current system info
-----------------------------------
Current image name: R80_992002773_20_50
Current image version: 773
Previous image name: R80_992002691_20_40
Previous image version: 691
Default image name: R80_992002639_20_35_def_220328
Default image version: 639
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You can use Factory Reset to make the default image current again, but for the previous firmware you use CLI - either the revert command:
> revert to
previous-image - Revert the system to the previous software image
factory-defaults - Revert the system to the factory defaults
You can also manually select the previous image to install:
[Expert@]# firmware_ver.sh -v
80 20 50 992002773 /dev/mmcblk1p1 80 20 40 992002691 /dev/mmcblk1p4
# firmware_ver.sh
Usage: firmware_ver.sh [-d <url> <image> <chksum>|-r|-v]
-d : Download from given URL to given path and verify checksum
-r : Revert to saved image
-v : Display firmware versions
CCSE / CCTE / CCME / CCSM Elite / SMB Specialist