To install Stock rom without pc or computer you need to have a rooted phone and a custom recovery install. Follow the steps given bellow and you can follow the YouTube guide:-
- Install SuperSu.
- Download FlashFire. Click here to download.
- Download Stock Rom. Click here to download.
- Grant root permission to Flash Fire
- Click on Plus icon
- Select the 3 no. Icon (firmware package Install)
- Scroll and select your Stock Rom from the folders.
- scroll down and click the flash icon