Help please with filing amended return

Help!  Two days ago I e-filed my return (federal and two states IA and NE). I am a NE resident but have farm rental income from IA.  Returns were accepted.  Today I received a revised 1099-B from one of my investment firms.  They made a correction and issued a 1099-B to my overall 1099 (Misc, D, I etc) for this one account.  It was triggered by one stock transaction in which I told a stock for a loss.  The loss significant enough to result in a tax refund.  The original 1099 did not have a 1099-B as this was the only stock sale transaction.  This new 1099-B is the only change to what I originally filed.

 

What do I do now?  How to I file an amended return?  Do I open the original TT tax return that I already e-filed?  Do a download the one account from my brokerage (I had numerous accounts from this same brokerage along with other brokerages on my original return?  Or do I manually enter just the new 1099-B info for this one brokerage account.  I have no idea how to start an amended return?  Can I hold this and adjust for the stock loss next year?  I use the desktop version of TT Advantage Premier for MAC

 

Someone said I should wait 20 days to file an amended return?

Thanks so much for your help.

Gary