This is not so much asking or help as it is pointing out an error in your code.
You have the HTML form name of “exercise-form” with an input name as “:_id” which is probably just copy and pasted from the parameter url. You can’t access this from req.body.:_id because ‘:’ will throw an error. It’s something that may confuse people when they can access it from req.body and took me a few minutes of trial and error to figure out. Unless you meant for this to be an issue to teach us quality assurance practices.