I stand to be corrected but think your only option is the long winded one of moving all your sub-forums to the new top-level parent. Then you can delete the existing, and now empty, "Long Island Scoop Forum" sub-forum and finally, rename the new parent you have created that that of the deleted sub-forum.
Volunteer Helper - but recommending that users move off the platform!
Once the admin for GregHelp now deleted.