What to do if i accidentally shallow small pieces of glass?

Don't do anything. If the pieces were small enough that you didn't notice or had no pain on swallowing, no harm will come. Contact your doctor if you notice blood in your stool or from your rectum in the next 2-3 days, but probably won't happen.

Most of the time, that piece of glass will eventually pass out in stool without causing any problem. If you do not have any residual symptom after the accident, i.e. pain with swallowing, persistent epigastric (upper abdomen) pain or apparent bleeding from the upper GI tract (bloody vomitus or melena stool), you should not worry much. If you have any suspected symptom, you should see a GI doctor.