Can anybody tell me how to find

Here you go:
Get inside a specific list by going to Lists>Lists> Choose the list you want and click to get inside.
Once you are in click on "View Subscribers" the first square box.
Then in the section above the email column put in the email you want to search and then enter.

You will find the email address you are looking for. From there you can edit or do other things to the subscriber.

All the best!