To set the strap, please refer to attached photo.

First, choose one of the legs then set the circle in to the leg. Tighten the circle until it fix.
Second, open the circle on the other side, to loop all three legs in, and then tight up the belt.

Please be noted, the belt can set in any place on the tripod, therefore, please make sure the circle is on a right place with protruding which can stop slip.