Apart from the magic that admins can do for you (eg restoring from backups or doing something at the backend database), there are not many tools to allow you to bulk add observations.
But there is a batch facility that one can use on ones own observations, but it doesn’t work so well if you’ve got thousands to add. The batch adding needs to done from each student’s account when they are logged in to the website:
First rejoin the project.
Then click on your profile page
Click on observations (on the left hand side)
-it will bring up a list of your observations in the old iNat format, a page at a time (defaults to 30 at a time)
Click on the ‘batch edit’ button
Click on the ‘select all’ link (or tick the ones on the page that you want)
Click on the ‘Add to project’ button (about halfway across on the same line as the two previous options)
Scroll down the drop-down list and click on ‘Add’ next to the project you want
It will batch add that page (with a bit of a delay), you will have to do a page at a time if there are lots