What happens next?

How to save watermelon seeds for planting
Collect watermelon seeds from ripe, healthy watermelons.
They generally ripen 35 to 45 days after the plant blooms.
When the watermelon is ripe, the curly tendril on the vine will dry up and turn brown and the white spot on the bottom of the watermelon will turn yellow.
The watermelon will also lose its shine and become dull-looking. Do not collect seeds from watermelons growing on vines that have wilting, spotted or dying leaves or vines.