Take into account that one of the parts has a notch and the other a groove to secure the handle to the scraper.
Place the scraper into the opening of the plastic lid so that the handle notch fits into the scraper groove.
Turn the handle to the left until it stops (about a 1/4 turn).
Pull down on the scraper from the handle creating a gap; this locks the handle to the scraper.
You can also watch the step by step video.