IRS reached out me and asked me to pay additional tax for 2017. As I have a service for audit defense (both '17 and '18), can I use it for defense this IRS request?

[Critter]

If you purchased Audit Defense for your tax return, call Tax Resources, Inc. at 877-829-9695, or report your notice on their web site at http://intuit.taxaudit.com/. Do not contact the IRS. Let Tax Resources contact them for you.

This is the membership email you should have gotten:  https://ttlc.intuit.com/questions/1901569-when-will-i-get-my-audit-defense-membership-kit

If you did not purchase Audit Defense:

TurboTax has a special phone number for help with IRS tax letters, which will be easier than going through regular Customer Support.   At the page below, click on the blue button that says "Get Help from TurboTax Support".  Then it will ask you what tax year is your letter.  Then it will ask you what the letter concerns. Then it will show you the phone number during posted business hours.

https://support.turbotax.intuit.com/irs-notice/audit-support/

Also see the following link on the IRS web site for more help.
http://www.irs.gov/Individuals/Understanding-Your-IRS-Notice-or-Letter