In case you are not using notepad or any other editor that helps you change files encoding this tool can help.
you just need to have npm(version 5.2+) on your system.
npx persian-subtitle-fix -I path/to/file.srt -O path/to/outputFile.srt
in case you want to make it available on your bash you should install it globally
sudo npm install persian-subtitle-fix --global
Also if you don't provide any flags in cli you will enter to interactive mode.