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.