If you want to permanently fix the timing of an out-of-sync file, you can use online tools like the Happy Scribe Subtitle Shifter or software like Subtitle Edit to shift the entire timeline and save a new, corrected file.
: Go to Tools > Track Synchronization to enter a specific numerical offset in seconds. Permanent Fixes subtitle Flatliners.2017.720p.BluRay.x264.[YTS.AG]
If the subtitles are slightly ahead or behind the audio, you can fix them in real-time using VLC Media Player: If you want to permanently fix the timing