[U-Boot] trigger automatic update (FIT image) from prompt instead of "updatefile" env variable

Is there a way to manually trigger an automatic update using a FIT image, based on the way described in doc/README.update ?

I mean beside setting "updatefile" environment variable, saveenv and reboot, but trigger it from U-Boot prompt resp. script ?

As far as I can see, update_tftp() is only called once during the startup, but not referenced by any command.

Use case: Disaster recovery update via altbootcmd.

Thanks in advance, A. Pretzsch