I'd suggest using an ounce or so of automotive ATF , in the event that the engine is seized , rather than wd-40 .
Also suggest that you make sure there is fresh motor oil in the crankcase , prior to trying to manually 'turn-over' your cool little engine !
After giving it a day or so to penetrate , old mechanics are prone to use a wooden dowel inserted into the s.plug hole , semi-lightly 'tapped' with a small hammer , so as to free up the rings &/or piston from the cylinder walls .