Q.4 o’clocks
What is the best way to dry and store 4 o’clock seeds from an existing plant to plant next spring?

After collecting your Four O'Clock seeds, let them dry out for a day or two then store in a cool dry place through the winter. Keep in mind Four O'Clocks re-seed themselves plentifully, so go ahead and leave some seeds on the ground where they fall. You'll probably see more of these little beauties the following year.
These articles contain more information about Four O'Clocks:
https://www.gardeningknowhow.com/ornamental/flowers/four-oclocks/four-oclock-plants.htm
https://www.gardeningknowhow.com/ornamental/flowers/four-oclocks/winterizing-four-oclocks.htm