Custom Date Entry on ASPX Form

I need a skilled front-end developer who can help me modify a date input field on an ASPX site I don't own. - The task involves allowing me to manually enter a custom date, instead of the current date and time being automatically inserted upon form submission. - This custom date should be entered in a hidden field on the form. - The modification needs to be done using browser developer tools. I do not have access to edit the site's files, so all changes need to be made on the front-end. Please only apply if you have extensive experience with front-end development and are familiar with ASPX sites.