@ian.hunt I believe Magix Notation was based on Emagic Logic 4, so you could check out the user manual here: https://www.scribd.com/document/455602768/emagic-logic-manual-mac-pdf

But I think their might not be a specific command to delete a bar, instead you probably need to cut that bar portion of your composition so that every MIDI event after it moves backwards in time.