After a lot of research and tests I have successfully implemented a web-page that reset the PlayFab password! As this is the first time I work with php, CSS, have very limited experience with html it has been a quite interesting learning experience.
However, in the ResetPassword API the Secret-Key is a requirement: "This API requires a title secret key, available to title admins, from PlayFab Game Manager.".
As I do not want my Secret-key to leak I would like to ask for advise hot to protect the secret key?
I have not yet tested Cloud Scripts but found this:
https://community.playfab.com/questions/44554/how-to-make-the-reset-password-function.html
...it looks like I can only use this function if I have an Azure subscription?