fastboot set_active command does not exist

I am trying to root my Xiaom mi a2 phone But i am stuck on changing the active partition When i enter fastboot set_active b it doesnt

Boot your smartphone into Fastboot Mode · Now, connect your smartphone to the PC using a USB cable · Open a Command Prompt, Terminal, or

fastboot_ error_ failed to identify current slot boot anymore and only fastboot is fastboot getvar current-slot current-slot: b Finished Total time: fastboot --set-active=b

fastboot getvar currentslot Display a bootloader variable fastboot set_active suffix: Sets the active slot If slots are not supported, this does nothing fastboot boot