My turbotax desktop says that my "amended" return was accepted. I am trying to convince the tax advocates that I have filed my amended return. How to get documentation?

Well--that makes no sense since amended returns have to be mailed, and they are not "accepted" or "rejected" the way an e-filed original return is accepted or rejected.  When did you amend it and how did you get it to the IRS?  

In a very recent development, it will be possible to e-file an amended return for 2019 soon, but not yet.  See below:

https://ttlc.intuit.com/community/amending/help/can-i-e-file-my-1040x-to-amend-my-return/01/26008

So not sure what you did or what you are seeing.  Are you really sure you are seeing the word "amended" in that message?  Or does it say the return was accepted?

Until e-filing becomes available for your 1040X here is the information that would pertain to the amended return you seem to think you filed:

The only way to file an amended tax return is to prepare a 1040X and print, sign. and mail it.  If you did something else, like try to e-file a change, the changes were NOT TRANSMITTED.

You can amend a tax return after it has been fully processed and you have received your refund.  You must work from your return exactly as it was when you first filed it. If you changed anything, change it back to the way it was when you originally filed it, before you follow the steps to amend. Follow the TT instructions to amend a tax return:

https://ttlc.intuit.com/questions/1894381-how-to-amend-change-or-correct-a-return-you-already-filed?jump_to=answer_3288565

Wait about 3 weeks and you can check the status of your amended return:

https://www.irs.gov/Filing/Individuals/Amended-Returns-(Form-1040-X)/Wheres-My-Amended-Return-1

It will take about 3-4 months for the IRS to process an amended return.

https://www.irs.gov/filing/individuals/amended-returns-form-1040-x/amended-return-frequently-asked-questions

And here is what is happening with amended returns that have been mailed this year:

   The IRS has not been working on mailed returns until very recently---and an amended return can only be filed by mailing it in.  Under normal circumstances you would be able to see something about your mailed in Form 1040X after about three weeks, but that is not the case right now.  The usual 4 months for processing an amended return is going to take longer.  Sorry.

https://www.cnn.com/2020/04/20/politics/irs-mail-trailers-covid/index.html

MAILED RETURNS

Per the IRS website IRS Operations During COVID-19: Mission-critical functions continue:  

IRS operational status and alternatives

Processing Delays for Paper Tax Returns: Taxpayers should file electronically through their tax preparer, tax software provider, or IRS Free File. 

We’re experiencing delays in processing paper tax returns due to limited staffing. If you already filed a paper return, we will process it in the order we received it.

Do not file a second tax return or contact the IRS about the status of your return.

 If you mail a tax return (or a payment) to the IRS, it is a good idea to use a mailing service that will track it like UPS or certified mail so you will know it was received.

 TurboTax will not know anything about your amended return, and nor will TT know that you put your 1040X  in an envelope and took it to a mailbox.  TurboTax does not get updates on mailed  (or e-filed) returns.

When the IRS finally opens its mail and begins to process mailed returns you can check the status on the IRS site.

https://www.irs.gov/Filing/Individuals/Amended-Returns-(Form-1040-X)/Wheres-My-Amended-Return-1

https://www.irs.gov/filing/individuals/amended-returns-form-1040-x/amended-return-frequently-asked-q...

I filed an amended return in April irs says its still processing but when I check turbo tax it says accepted and has a dollar amount but when I call turbo tax they have no record I checked my file and my added dependant isn't no where to be seen what is going on