Have you reviewed your 2015 Notice of Assessment, and determined that the income was not included by CRA? You may also wish to contact CRA to confirm that they have not completed a Reassessment to include the income, as CRA receives copies of T slips as well, and matches them up to the returns filed.
To call CRA, 1-800-959-8281
If you do actually need to adjust the tax return already filed, go here:
http://www.cra-arc.gc.ca/changereturn/