Hello again, the problem is partly solved...
This information will not help anyone.
If you enjoyed being helped, you should share your experience.
At least you should share which firmware you used to help another user in the future.
...anyone knows how to change the startup logo to your own?how to convert a .jpg file to a .nb0?
Try using this tool:
Spoiler: nb0 unpacker-packer tool
[Only registered and activated users can see links. ]

https%3A%2F%2Fimg.xda cdn.com%2FHWI2F5hlA9As rAe8oEQfuQ6YTk%3D%2Fhttps%253A%252F%252Fimg.xda cdn.com%252FdQSPE48j0qwp8owVmHY65T3 uR4%253D%252Fhttps%25253A%25252F%25252Fforum.xda developers.com%25252Fattachment.php%25253Fattachmentid%25253D4321665%252526stc%25253D1%252526d%25253D1509692252

Credits: heineken78 (4PDA and XDA)