That rubber thing slides in the track on your awning roller arm.
If you have an electric awning, you probably will never use the awning puller strap. If you have a manual awning, you absolutely need to use it.
I have 2 electric awnings and have straps on mine, because the awning is so tall I can't reach it. I can reach the straps and pull them down to make the awning tilt for rain. Standing on a short step ladder, I can hold the awning down (tilt) with the strap in one had, and lock the awning arm in the tilt position with the other.
Here's a 5 minute video that will show what the strap is used for. There are bunches and bunches of videos on YouTube that will explain anything on your camper.
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2019 Montana High Country 375FL
2014 Chevy Silverado Duramax, 6.6L Dually