You can e-file and amend your return later, or you can file for an extension and file your return when you receive your missing information.
If you e-file now and later amend your return, you will have to print your amended return and file it by mail.
If you file for an extension, then as soon as you receive the information you are missing you can add the information and e-file your return.
It is entirely up to you! Should you choose to file an extension, please look below for information and instructions:
https://ttlc.intuit.com/replies/3301811