assist (someone) with (something)

The word "assist" means "help" but is more formal. Use it with customers and other people that you need to speak to respectfully:

How can I assist you?

Can you assist this gentleman with his question?

I can assist you with that.

This is a sentence that employees at stores (like clothing stores, etc.) say to offer help to customers. They say this when a customer is waiting for another employee.

"I can assist you with that" sounds polite and formal.