I just went through this. It was a nightmare. So I called the IRS and they said there's a page to sign on the back of the page where your PIN is listed. I mailed it, but they said they never got it. So, go to IRS.gov/dutreply and enter your Access Code listed on the letter..(It seems the PIN is still the same even though the letter said it would be deleted).

For some reason the IRS hasn't updated their website, so when you choose a year and it's not listed (i.e. 2024 or 2025 as of now), then he said to just choose 2023 and they will sort them when they come. He said it takes up to15 days to process.

In case you still need help call [removed] (4:30 am-4 pm PST or 6:30 am-6pm CST), but the wait is about 1 hour to 1 1/2 hours, then they will send you to the 94x line and you have to wait another 40 minutes. I made the mistake of calling at 2:30 PST and when they answered at 4 PM, they said they were closed and to call back the next day, so call early! Hope this helps

Oh, and he said to also resend a copy of the letter (just in case).I don't have the envelope anymore, but found this address on the top of the letter which I will use: IRS, [address removed]. Good luck