Hold the fort.
[Idiom] HOLD THE FORT. - Learn to Handle Things on Your Own With Classic Idioms
Take responsibility temporarily.
The idiom "Hold the fort" harks back to the days when soldiers needed to defend a fort from invaders, requiring someone to take command in the absence of the main leader. Today, we use it in everyday situations when someone is asked to take charge or manage a place or situation temporarily until the usual person in charge returns or the situation is resolved.
Example Sentences
Mike had to hold the fort at work while everyone else was at the corporate retreat.
Mike had to manage things at work while others attended the corporate retreat.
When our manager got sick, I was asked to hold the fort until she recovered.
When the manager fell ill, the speaker was asked to manage things until she recovered.
Since the boss was traveling, Janet held the fort and made sure all deadlines were met.
Janet managed things while the boss was traveling, ensuring all deadlines were met.