Select a fabric glue. A good one is Tear Mend by Cherryhook. Put a dot about the size of half a dime on the cheek. Massage the ear three times a day with glue on it. Glue lasts around 2 days to 2 mo. Repeat as necessary.
Some breeders uses tacky craft glue. Placement is important and should be taught by an experience breeder. The ears must be opened weekly to clean or an infection could result.
Australian Shepherds generally don't need to have their ears glued. You should talk to a vet or an experienced breeder before trying to glue them yourself to avoid injury.