Verified answer

Tilt the mower back while it is NOT running and see if you can spin the blade by hand. I mean with no effort. If you can then tighten the blade nut. If this doesn't work take it back. If they don't fix it for free let me know so I never buy one.

the best way to determine the "direction" of a screw is to note the direction it works in!! take a hand held circular saw,, the blade rotates anti-clock was so the screw is threaded as a righty tighty! a table saw blade turns clock wise so to tighten the nut on it you turn anti-(lefty) to tighen it,,, whichever way the blade turns you have to go opposite to tighten this prevents to screw or bolt from working lose from the torque!! most american mowers are lefty losey!!! they WILL get tight because they are MADE to tighten up from the torque,, always spray with WD-40 etc and use a box wrench or socket with as many 'teeth' as possible to get a better grip and prevent stripping the heads or breaking a socket ,, and use at least a 3/4" drive socket

Check the cable or device that engages the blade you may need to

adjust for proper operation.