Hello Radu,
I do it follow you :
1. Program the rbf using DS, like you mentioned.
2. Power off the board.
3. Open the Boot Loader, load the configuration for S32K, see below the screenshot.
4. Reset the board using the rest button.
5. Start Boot Loader.
But I occur issue ,like this :

If the error is about the "status " in the "RAppID BL Tool " down.
thanks
Regards,
Feng