In windows for me it kept saying "id_ed25135: No such file or directory" upon entering above commands. So I went to the folder, copied the path within folder explorer and added "\id_ed25135" at the end.
This is what I ended up typing and worked:
ssh-keygen -p -f C:\Users\john\.ssh\id_ed25135
This worked. Because for some reason, in Cmder the default path was something like this C:\Users\capit/.ssh/id_ed25135 (some were backslashes: "\" and some were forward slashes: "/")