I'll try to answer your question in a step-by-step manner.
Firstly, if any mandatory question is left blank, you cannot submit the form. Specifically to the employment history, DoS requires previous 2 employers or the 5 year employment history. I don't specifically remember what the exact requirement is for the DS160. (while filing for an immigrant visa for my spouse I was asked for my 5 year employment history.) You may know that better since you just applied for it.
Now since you have already submitted the application, it will either be approved or be rejected.
If it is rejected based on an incomplete form/errors the embassy will reopen the form for you to correct all the mistakes or fill in missing information; and after you sign & submit it you will have to contact the US Embassy where you applied for specific instructions.
The Embassy or Consulate should reopen your DS-160 submitted after
April 1, 2010 if your application is denied for this reason and ask
you to correct it, as explained below:
- DS-160 applications submitted on or after November 1, 2010: Enter your application ID number and answer additional questions as
prompted to access and correct your application.
If your form is approved then I would suggest you take your resume/CV with you to the interview along with that employer's related documentation i.e. offer letter, experience certificate, paystubs anything pertinent to support your resume and establish that you were employed there. Ofcourse they will know your employment history. This may not be required and should be presented only if asked for.
Furthermore, the officer will know your employment history and you may (infact will) get questioned about it.
Further-even-more, another way could be to submit a new DS160; but I don't think this is as much of a huge mistake (like passport number, name, DOB etc) that you need to submit a new one. But if you want to look into the possibility:
While it is not possible to change information on a DS-160 after it
has been submitted, there are two easy options for creating a new
DS-160. If it is within 30 days from when the original application was
submitted, the first option is to log into the CEAC system and select
“Retrieve an Application” using the application ID number. Next, you
will be asked whether you want to go to the confirmation page or
create a new application. Select create a new application, and the
entire application will appear, except for travel plans to the U.S.
Then, you will need to edit and update the information and submit
again. Alternatively, if you saved the DAT file from the original
application, you can access and amend the information at any time from
an already submitted application. Once the changes have been made,
save and submit the new application. For either option, if the
original DS-160 was used to book the visa appointment or pay the MRV
fee, the applicant MUST present at the interview the confirmation
pages from the new AND original DS-160, as each submission creates a
And ofcourse you will have to pay the processing fee (if any) again too.