Who knows ho to do that without any addons?

Use audacity, free program. Or try to find an online converter.

Format facotory

orr open the mp3 file with win rar rename the extention .mp3 to .wav in the adress bar [it worked for me but not soo sure]

No kooper , usually it corrupt the file.
Use program such as Audacity.

It do still works for me,

Online convertors work just as well for me. I've used the below online sites without issue:

http://media.io/
http://audio.online-convert.com/convert-to-wav

Here use this: http://audio.online-convert.com/convert-to-wav I used it to make my kiai sound.