The problem with UEFI is that the EFI System Partition has no letter which you need to use to point to other than the 'live' BCD.
EasyBCD's functionality was all designed long before UEFI was even dreamt of. Although it has been comprehensively updated to be fully EFI compatible, a lot of function has been deprecated from the bootmgr.efi code by MS so the full power of EasyBCD is not all available on modern PCs. Nothing can be done to circumvent the MS prohibitions.
There are no letters, drive numbers or partition numbers in the BCD.
It addresses partitions by a UID which is a hash of the unique device signature combined with the partition offset from the start of the disk.
One of the many things EasyBCD does for you is translate that user-unfriendly string of characters into a Windows letter by looking it up in the registry device table where the OS specific map of device letters is stored. That translation works both ways, enabling you to tell EasyBCD the letter and it will translate that into the UID for you.
Under UEFI there is no letter associated with the UID for the EFI System Partition in that table.
EasyBCD knows where the live BCD is so you don't need to point to it, but if you want it to navigate to somewhere else, you need to have some way of telling it where.
One of the reasons EasyBCD was written, way back in the time of Vista, was to give the end user a friendlier interface with the BCD than that offered by MS bcdedit which is a command line utility which does require you to look up and accurately type the complex UID in every command.
As I previously said, it was designed and written before UEFI was even dreamt of, so a tough job to anticipate future architecture changes.
I use either DiskGenius or Aomei Partition Assistant to assign a drive letter to the external EFISECTOR partition, then I can use EasyBCD's "select BCD store" to edit them. Or, since it's easier, I just use DiskGenius to copy the BCD to my desktop, edit it there, then copy it back, overwriting the one I first copied. EasyBCD automatically loads the BCD from the running system, even from the hidden EFISECTOR partition, so this applies to external BCD stores only.