Calm down, my friend. I'll explain the step-by-step how to do it.
1- Download the application for windows called Odin, it will be used to make the rom flash and also the recovery. You can download it from this link or search on google.
https://odin3.en.lo4d.com/windows
2-Download the rom of this website
https://updato.com/ so do not have the version LL 5.1.1 for your country, download from another that uses the same language as yours. I advise using a download manager because the file is large, to prevent it from being corrupted.
3- Downloaded the two, use the odin to make the new rom flash for your device. If you do not know how to use Odin, search google on video tutorial how to do.
4- Download recovery from this site
https://cloud.mail.ru/public/6rpR/DVFmGdmW3 (thanks to SHEV T). Download the file in .TAR that is compatible with Odin. Make recovery flash, the process is the same as rom.
After doing these procedures, you will have the recovery that will allow flash of any rom compatible with your device. These steps also serve to reinstall the official rom in case of problems.