By design, users with edit right for a module instance can only edit/delete those events they created, not those created by others. To achieve this, set their security group as moderator of the module instance (with the "Moderator Role" select box in Event Module Settings > Moderation Settings).

BUT CAUTION: There's a ... well ... "undocumented feature" with this setting (but luckily there's a workaround, too):
Setting a moderator role will make the module disappear from the page for all but the Super User (=Host). If you log in  as Super User and go to the module settings again, you'll see why: the "Inherit View permissions from Page" checkbox in the Permissions section is now unchecked, so that not even the portal admin can see the module now! As a workaround, check the "View Module" checkbox for all users.

More info in this post: "Assign Moderator Role - Module disappears"
Many thanks to secret.squirrel for investigation and finding the workaround!

I'll check if this issue has been reported to the bug tracker already, and I hope we can fix it for the next version.

If you have deleted it by mistake, restore it from your recycle bin under the admin account.