I found out what my protector alters did by looking at when they came out... the kind of alters that come with dissociation have their own sense of agency (what they do, how much control they have, and a bunch of other things too) the key to finding out what the alters sense of agency is, is by looking at when and why they came out. you said one came out recently, why did they come out (what triggered you to dissociate, what was the reason they had to come out to take care of things for you?)

Example when I knew Rainy had come out I knew that we had had a rain storm. that told me that Rainy protects me from rain storms/ thunder storms.

All alters are protectors in one way or another. so when you are looking at trying to find out what they do to protect you, look at why they came out. that will answer the question of what that alter does to protect you and from what.