File uploaded but form not submitted

Hi there, I am asking your help to figure out this situation.

Let's say I built a file uploaded system using dropzone. I did all the stuff like:

• Include dropzone css and js in view file
• add post route to custom endpoint and point to a controller
• add logic to handle uploaded file and upload it to file system and return the file name as json response

Now here is my question. If user uploaded a file and after that the user closed the browser tab (User don't want to save the post).

Can you tell what if I want to handle the situation when people upload the files on the form but then don’t hit final Submit. It means that the files are still stored on the server.