You will need to amend your return, once it has been
accepted and any refund due has been paid out. Then, you will go back
into your return (following the amend instructions) and find your name in the
Personal Info section. Click to edit beside your name. On the following screen
near the bottom, you will find the area to click that you can be claimed as a
dependent by someone else. I will attach a screenshot of that area, so you are
better able to locate it.
Your mother will need to prepare her tax return and file it by mail, as the amended return will need time to be processed before her return can be processed properly.
Please see the following TurboTax FAQ for instructions on how to amend your 2016 tax
return in TurboTax.
https://ttlc.intuit.com/replies/3288565
