You should definitely go to a local tax professional for help. A lot of what you are saying here is not clear, and there is a lot of detail missing. When you meet with the tax pro bring the entire letter with you. The tax pro can read the letter that you received and can, with your permission, get a copy of your 2022 tax return from the IRS if you don't have a copy. You cannot file a Form 1040-X without having the original tax return.
You can access a copy of your 2022 1099-B on the Fidelity web site.
