Turn off the garbage disposal, and disconnect the power, which is the only way to ensure that the garbage disposal does not accidentally get turned on while you are working. Don't ever put your hand into the garbage disposal. Instead use tools such as tongs or needle-nose pliers to remove objects from the disposal.
Ask a helper to hold a flashlight above the garbage disposal so that you can locate where the popcorn seeds are. Unfortunately, this is a tedious process because it will require you to remove the seeds lodged in the disposal one at a time with the tongs or needle-nose pliers.
Reconnect the power, turn on the hot water and turn on your disposal to listen for anymore popcorn seeds rumbling around. If there still are seeds, repeat the seed-removing process. If not, continue running the hot water and grinding the disposal for about one minute.
Seeds or bones of any type can ruin a garbage disposal. If you find that your disposal still is not working after picking out as many of the seeds as possible, you will need to call a professional. You may need a new garbage disposal installed.