Thank you for your request, Ly Hoang Oanh.
It is not possible to just delete some revisions, so you did the right thing by rolling back to revision 2 in revision 4.
Now the problem is that you uploaded as a.txt file what is actually a .sbv file. So I took the liberty to recreate the .sbv file from your subtitles and to upload it as revision 5.
I hope that's OK for you?
Thank you so much for helping me out! ^^
Ly Hoang Oanh
Please help me removing the versions of the Vietnamese subtitles of this following video, except for the version 2:
I have to remove them because the first version is not a completed subtitle, and the third and forth ones have wrong timing. The second one is completed, but can you tell me how to sync the timing?