Hey there! Happy to help.
Check out this link that has the contact info for the Seneca Enrollment Department: http://sctribe.com/service/enrollment-department/
You can also download the application from this site. Looks like you’ll need your birth certificate and SSN card, plus you’ll need to fill out a family record form, which looks like you’ll need their roll #’s too, which can be found on their tribal membership cards.
If you need help, just call the number listed on their site. That’s what they are there for.
Happy enrolling!
Auntie Manda