How do you "Unassign" a commander who's with a core unit. In the partisan battle in Red Storm, it's a primary objective to unassign commanders by turn #2 and I can't seem to get past this!! Any help greatly appreciated!

In OOB how do you unassigned commanders. It's a primary objective in the Red Storm scenario whereby commanders must be detached from core units. I can't seem to find how to do this! Can someone explain how?

Thank you! Much appreciated

My question relates to gameplay and creating pontoon bridges. Could you help describe how this is done? When I deploy and engineering unit (US orBritish), adjacent to a river hex, do don’t know how to create a pontoon bridge. Does the unit need to be in a certain hex for a number of turns? Thank you...