nothing
The command del "\?\c:<path\longfilename.ext>" was written syntactically. That is, you would replace <path\longfilename.ext> with the copied path. However, I see you entered the command correctly in your previous post and got "cannot find the file". That has me puzzled.
If you are on a computer where you can install software, I suggest trying to delete that file using a tool that can work directly with long paths, such as the 7-Zip file manager.