“Can you tell him to swing by my office when he gets a chance?”
You want to talk to one of your co-workers. You go to talk to him, but he's not at his desk. You ask another co-worker to give him a message, and the message is like this.
Can you tell him to swing by my office when he gets a chance?
"Swinging by" a place means visiting it quickly before going somewhere else. It's very similar to "stopping by":
But when someone says "swing by", it's even more casual and the visit sounds even shorter. You can tell someone to "swing by" a place when you want the trip to sound short and easy.
When you ask people to do something, this phrase lets them know that they don't have to do it immediately. They can do it at a time that's convenient for them.
Here's an example:
Can you help me with this when you get a chance?
If you leave "when you get a chance" off, it sounds like you want immediate help:
Can you help me with this?