I forgot to claim my union dues and already filed my return

[AndreaC1]

If you have already e-filed, you will need to wait until the IRS has accepted or rejected the return before you can make any changes to add/remove anything. 

• If they accept, you will need to wait until the return is processed and you have received your refund and then amend. If you owe them, pay them first and then amend. 
• If they reject, you can add the union dues and re-submit the return. 

Once the 2017 amend option is available, 2017 will become a clickable link below. You can then click it for instructions on how to amend the return. 

And when you are ready to amend, go here Can I deduct union dues, and where do I enter them in TurboTax? for steps on where to enter the union dues.

NOTE: You must have itemized to get this deduction. Job-related expenses (including union dues) are not fully deductible, as they are subject to the 2% rule. More info

How to amend (change or correct) a return you already filed

https://ttlc.intuit.com/replies/3288565