You need to call the IRS. I just had this problem and here's how I fixed it. I'm posting this answer because I struggled to find it on the QB Community.
Call 1-866-255-0654, Option 1, Option 2. I was on hold for about 30 minutes before I was transferred to the 941 department. Then I was on hold for another 1.5 hours. Explain to them that you updated QuickBooks and the 10 digit efile PIN disappeared. You don't know what the number is and you need a new one mailed to you. By the way, the IRS website says this can take up to 45 days. The owner of the company will need to speak to the IRS or you won't get anywhere with them. You'll need to provide your EIN, name of company, address, and telephone number. Once you're through, they'll give you a Case #. You'll only receive your 10 digit PIN in the mail within 45 days, so plan accordingly if you have forms due before then. You may need to mail in the forms if you don't receive your PIN in time to efile.
It's a pain, but this is the only way around it.
