As, Kathy, mentioned the feathers need to be trimmed around the vent to allow better viewing of the area.
I have had a few similar to yours, and sometimes the tissue can be lubricated copiously and pushed back inside, similar to pushing your pant pockets inside-out, but due to the fragility of baby birds, this can be hard to do without damaging the tissue, or bird. Strict cleanliness of the environment the birds being kept in, as well as your hands, need to be practiced to prevent infection of the tissue, which can occur fairly quickly with young birds.