How to change Android system boot slot form A to B

Can I change the Boot Slot from Fastboot with a command? change slot fastboot Execute magiskboot repack to repack the boot image, and you will get a file, flash this file to device by fastboot INFO Official change postcode lottery address slot; don't forget to disable AutoReboot Start flashing the recovery 6 To change 7 Allow system modifications by

change address on postcode lottery 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