I tried to talk with a representative about my 1099R from DFAS. My disability rating was raised to 100%r AS OF 30 Oct 2020.. I wanted to know if I could reflect that change on my 1040 or will I have to file a 1040X later.

It might be best to e-file your Form 1040 now without the adjustment to avoid any delays in your refund. And then file 1040X later after the original return has been processed. Please see  FAQ How to amend a tax return for instructions.

You will have to file a paper return to include all documents from the Department of Veterans Affairs and any information received from Defense Finance and Accounting Services explaining proper tax treatment for the current year.

Please see IRS Special Tax Considerations for Veterans for more details.