Perhaps a little more explanation would help (as would a power jack):
1. Extend jack to raise tongue above the hitch ball.
2. Back tow vehicle to place hitch ball directly under the coupler on the tongue.
3. Retract jack to lower tongue onto the hitch ball - then lock the coupler.
4. Extend jack to raise the tongue enough to lock the WD arms in place.
5. Retract jack, finish connections (safety chains, electric, break-away brakes)
You should not have to lift the tongue to put the coupler on the ball and by using the jack you need little or no force to properly connect the weight distribution arms.
If you bought from a dealer they should have gladly showed you the whole process. If not, find a neighbor or acquaintance (or even a random camper) to show you how to use power to avoid having to use super strength.