How do file for a cash advance on my tax return?do I just complete all of my information and submit?

When you file at the end it may be offered to you.  Not everyone can get it.  You can't self select it.  Then you don't get it until AFTER your efile is Accepted by the IRS.  This link explains it all and the amount you can get.  Read the whole page and the FAQs listed....

https://ttlc.intuit.com/community/refunds/help/about-refund-advance/00/27333

The advance has to be offered to you.

https://turbotax.intuit.com/refund-advance/

Refund Advance eligibility

Here are some of the eligibility requirements to qualify for a Refund Advance loan:

• You’re 18 or older
• Your expected federal refund amount is $500 or more
• You’re not a resident of North Carolina, Connecticut, or Illinois
• You’re e-filing your federal tax return with TurboTax
• Your physical address is listed on your tax return. Your address must be located in one of the eligible states and can’t be a PO box or prison address
• You’re not filing one of these tax forms: 1310, 4852, 4684, 4868, 1040SS, 1040PR, 1040X, 8888, or 8862
• You aren’t filing on behalf of a deceased taxpayer
• You must report income on a Form W-2, 1099-R, or Sched C
• You must open or have an existing Credit Karma MoneyTM checking account1.