I was stymied at first. Then I recalled we were operating under the Articles of Confederation at that time, and the new constitution was being sent to the "President of Congress." (The Continental Congress.)
That brings up the old trick joke of "Who was the first President of the United States?" Some say John Hancock. Wrong. Some say George Washington. Right. George Washington is the right answer because he was the first president of the United States under our present constitution, and before that, the "presidents" were presidents of congress.
There were a lot of presidents of congress, starting back in 1774. Mostly they changed with each session of congress, more or less. They were more like an elected chairman of a committee rather than the "grandeur" of our current system. And John Hancock was, indeed the president of congress on July 4, 1776. But he wasn't President of the United States like now, and he wasn't the first president of congress, either.
The first president of congress was Payton Randolf and the last was one Cyrus Griffin. In between were 14 others (two were duplicates), including the aforementioned John Hancock. Also numbered among those early, rather fleeting in terms, presidents were John Jay, who would become our first Secretary of State and, later serve on the Supreme Court; and Richard Henry Lee of Virginia, ancestor of Robert E. Lee. Randolf and Hancock each served two terms each, both non-consecutive.
So it was president of congress number 16, Cyrus Griffin, that the cover letter signed by George Washington was sent, along with the new constitution. Griffin dutifully put the matter before the congress of that time, and the new compact was passed and sent out to the states for their concurrence. Griffin stayed on as president until George Washington was sworn in under the new constitution on April 30, 1789.
One point of interest: one of these old congressional presidents, number 15, was Arthur St. Clair. He was pretty famous and pretty interesting. I won't go into his life here, but he came to America from Scotland, as a British soldier, during the French and Indian War (the 7 Years War, as the British call it) and is the only American president of congress who was born on foreign soil. He was born during the latter stages of the Jacobite Rebellions and his family moved because of them, and that is why his name came to my attention.
I am aware that one of the things other countries hate about Americans is that we always are talking about our Wonderful, Glorious, Constitution and saintly Founding Fathers. A lot of them don't think too much of our constitution as anything special, and are sick of hearing about the traitors who were our founding fathers. To them, I hope they are not offended by this post.