A vet or a groomer can empty the glands for you.
Usually the fiber choice works better after the glands are emptied as the fiber helps keep the glands emptied as the dog passes bulkier stools.
You can read about the anal sacs here
and you could empty them yourself though it smelly and the dog often can use a bath afterwards.
Groomers typically routinely empty the glands among other things as a part of a grooming process so you might see if a groomer was a less costly option than a vet visit for this. But if the sacs are infected a vet visit may be a better choice to get meds if needed to help with the infection after the sacs are emptied.
Hope this helps you!