Since you filed a return last year your AGI should not be zero, regardless of who you used as your tax preparer. You can either get your AGI from your 2016 tax return (see FAQ below for instructions) or to confirm that you are using the AGI the IRS has on file (every now and then it differs from what is on your return), you can quickly download a free IRS transcript of your return from the IRS website which will include your accurate AGI. Select the blue link above then 'Get transcript online'. On your transcript, look for ADJUSTED GROSS INCOME (you may need to look on page 2). This is the number in the IRS database; make sure the AGI you enter matches this number exactly.
Please see this FAQ for how and where to find your AGI on your tax return: https://ttlc.intuit.com/replies/3301618