How to change Android system boot slot form A to B

It can be very useful to know if partition slot A or slot B is currently active and you can learn

But I want without fastboot command My usecase is the bootloader need to check the currect active slot and set the proper suffix How can I

fastboot getvar currentslot Change CSC with one click; Remove FRP for new security patch Auto-detect file and select slot; Auto-extract for ZIP file; Ignore MD5

fastboot_ error_ failed to identify current slot I never even knew that you could use fastboot with a locked bootloader! Learned something new