Well, if you have already received an acknowledgement of your application then you can mail a completed form mentioning the reference number so that it can be filed properly. USCIS is not so good at filing paperwork submitted like this and it can often get lost.
Alternatively, you can just wait. When USCIS does not receive complete documentation with an application, it will send a letter asking you to submit that. That letter from them will also contain detailed instructions on where to send it and how. At that time, you can do it. That will make sure that it is included in your file.
If for some reason you are rejected, you can still reapply because you are not ineligible, you just failed to complete the paperwork properly.