I'm getting a job in Canada for 2 years. If I apply for reentry permit in US,?

but then leave before my biometrics, can I go back to USA for biometrics when it is time? Do I need to send in my Green Card with the initial I-131 application? Or can I use my Green Card to enter USA for biometrics appointment. Without my Green Card I cannot go to USA as my nationality requires a visa. So all I want to know is whether you send in your green card with I-131 application before the biometrics, or do you get to keep it until your reentry permit is approved?