As more than 60 million votes have already been cast in the 2020 presidential election, we see that "Google searches for "change my vote" have spiked over the last several days " as reported by New York Post.
Apparently the scandals involving Joe Biden and his son Hunter have started to filter down to those that are not online political junkies, despite the attempts by the media and social media to hide the news from their audiences and users.
Note: States have their own rules, so it is up to each individual to look those laws up and see which states do allow voters to change their vote and how to do it.
For example: In some states if a voter voted by mail, they can physically go to the polls and cast their changed vote, but if their initial vote was cast in person, they are out of luck and the vote cannot be changed.
More on specific states and their rules for changing their ballots can be found in the NYP article.