You can gently rub that out with a wet Q-tip. That's eye gunk that solidified, probably while he slept. One of mine kept getting them for weeks, he had to be treated with a triple-antibiotic ointment twice a day for a week. Now it hasn't happened since. Also see if your cham is getting enough vit A, there's always a small chance that it could be deficiency related. I supplemented mine with a drop of vit A capsules for 2-3 days just in case as well.
Be gentle, but you can get that out if you feel confident about doing it. Better he rubs his eye against a Q-tip to get that out than a rough vine.