Postal letter or email? How did you happen to get such a letter? Are you certain it is from TurboTax? One always has to watch out for scams these days.
Are you an Advantage member with an annual subscription for TurboTax product? And if so, is it asking you to update/verify the information in your Advantage account so that you can be billed in early November to get the 2019 product when it is released in November?
If that's your situation, then please see this FAQ on how to update/confirm an Advantage account: