What do I need to do to make it to where my state tax return can be efiled instead of mailed in?

Did you efile the federal return yet ?   And if so was it accepted for processing yet ?

Yes and yes

What happens when you try to efile the state return?  Is there an error message?  Or did you try to efile, and it was rejected?
Or do you just need to know how to open the return back up so you can proceed to change the filing method and efile?

It will not let me seeing it to e-file. what do I do?

So is the answer to my last question above a Yes?   If so, we can tell you how to open it back up.   See the steps I left in the Answer section below.

As long as you have not actually filed yet (not mailed and not successfully efiled), here's how to open the return back up to change filing methods if TurboTax thinks you are finished:

• Log in and go to "Your Tax Returns & Documents."  Click that line or the word SHOW to expand.
• Under 2017 choose "Add a State."  (you don't really add one; that's just to get the return to open up.)
• Once the return is open, go through the REVIEW tab to be sure all is still in order.
• Then go through the FILE tab and change the filing method to "efile."  Choose to efile only the state return.
  
• Then be sure you go all the way to the end to the final screen and click a button "Transmit My Returns Now".
  
  

NOTE:  Do NOT use this method to open a return to make changes/edits to an already-filed return (one that has actually been mailed or efiled.)   If you later need to make changes to an already-filed return, you have to go through the formal amending process, and your return must start off exactly as originally filed.

Federal return efiled and refund received.