By accident, I delete 2 of the Meeting ID 21 and 31. How I can get it back? Otherwise,

all meeting data should have 13 items, but mine is 50. How to fix it? Thank you
Sorry you're stuck but there's almost always a pretty easy fix! Do NOT try to start all over again, uninstall Max's Pitch Package, etc. That can make it worse. There's a 95% chance the same snag/fix is listed & answered in the Help FAQ. But if you can't find it there, post your problem here.
Make sure you post in the right category below & be sure to include a screencap showing the issue!
Well it looks like you repeated the data import multiple times. You should only have 10 Meeting records, with IDs of Mtg-01 through Mtg-10 so you could delete all the Meeting records above Mtg-10. Why do you think you want to undelete Mtg-21 and Mtg-31? All Meeting records above Mtg-10 should be deleted.
If you really want to undelete, let me know and I can tell you how.