Take your freewheel off your cranks, the threaded section that the freewheel came off, slide the ring onto that section then screw the freewheel back onto the cranks. Therefore the freewheel holds the bashring onto the cranks.
I've attached an image to help you.
Are you cranks 160/5mm or 170/5mm?
They can be, there's a tutorial on Tartybikes that'll help you out!