Checking Android's Currently Active Partition Slot

How to change the current active partition slot? fastboot set active slot fastboot commands :- https How to Check and Change Current Active Slot on Android fastboot set active slot Advanced features include Active When placed in an HDMI slot on a television set or computer monitor, the device turns that display into a personal computer

fastboot_ error_ failed to identify current slot fastboot getvar current-slot current-slot: b Finished Total time: fastboot --set-active=b Setting current slot to 'b' OKAY