Thats done from the File > convert menu. Now you know the sync adjustment, did you check carefully or spend time adjusting it.
I think via it's info while playing a video it will show for some media containers by how much the sync is out. Then test in different places on the video for same sync value. If same it'll be easy to fix with vlc.
File > convert slect your file then conatianer video and audio. On audio is where you can set the new sync, enter file output name and save.
Though if mpeg 1 or 2 you best use something like projectx which if remember can do that all for you. This info is from years ago, maybe now there'ssoftwares to do this easily now. Software that can load any video and automatically tell you by how much and where in the file is out of sync. Even maybe smart enough to fix the sync even on those vhs capturd type sync's. That can go more out of syn over the duration of the video (possibly the hardest to fix).