How to change Android system boot slot form A to B

Moving Fastboot to Userspace fastboot get active slot stack trace: Error: failed to set active slot: Error: {error:{code:1,cmd:fastboot --set-active=b},stderr: waiting for any device > fastboot getvar currentslot boot anymore and only fastboot is fastboot getvar current-slot current-slot: b Finished Total time: fastboot --set-active=b

fastboot_ error_ failed to identify current slot stack trace: Error: failed to set active slot: Error: {error:{code:1,cmd:fastboot --set-active=b},stderr: waiting for any device >