If you filed a return for 2015 you can use your AGI or PIN from 2015 the IRS is not giving PINs this year.
To find your AGI you will have to go to 2015 return, depending on which 1040 form you used the amount will be on that line.
If you used:
1040-line 37
1040A-line 21
1040EZ- line 4
1040NR- line 36
1040X- line 1 Column A
I hope this helps you.