nope, there's no legal authority granted to him to do any such thing... any ratifications to the constitution itself require a whole new constitutional convention to vote on, and that can't happen unless at least 34 states vote to hold another convention... the best he can hope for is using coronavirus as an excuse to delay the election, but that's in early november, and hopefully, this should all be cleared up by then
and also, the states are responsible for organizing their own elections, so i'm pretty sure even with that, all he could do is recommend that they be delayed, but he wouldn't have authority to tell any state that they had to