If I remember correctly the two halves should separate so you can get the propane tank on the support shelf. When you wrap the two straps back to the front the right side strap (looking at the picture) should have a bend/hook on the end that will connect to the end of the white solid piece. You then push the straps tight to the tank and you should be able to snap the solid piece over the white frame piece pushing to the left. The holes are to adjust the tension if needed. Kind of a cam locking system.
I'm sure this is clear as mud but its difficult to put into words.
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