Unlawful Presence and Overstay H-4 Overstay of 13 Days. Need Urgent

Hi,

1) I am on H-1 B status & our(me-H1B, my wife & daughter-H4) stamping was valid till 4-Sept-16

2) My employer filed for H-1B extension & I got it approved till 15-July-18.

3) I realized on 14-Sept-16 that my family's extension should have been filed separately. I was under the incorrect impression that my H-1 extension would be sufficient for them to stay. My employer said they only file H-1 extensions & not H-4

4) My family left US on 17-Sept-16 (after 13 days of overstay).

Now I am planning to apply for their visa stamping using dropbox. My questions are:
1) How can I correct my mistake? Can we write a letter to USCIS? When should we present it to them?
2) It happen due to oversight in DS160 form what should we state about overstay? Shall we include apology?


Please help me out.

Regards,

Unlawful Presence and Overstay H-4 Overstay of 13 Days. Need Urgent