My credit report only comes from the Experian. While most business use Transunion, do anyone know how to report my credit to Trans union?

They will not accept a report from you. They only accept reports from businesses and government agencies.

They probably already have a report on you, same as Experian.

Go to AnnualCreditReport.com for all 3 free reports

YOU cannot report YOUR credit to anyone. It is up to the creditor who they report to OR if they want to report at all. There is no law that they must report your activity and they are certainly not going to report to who you want them to.

One or both of Discovers scores are Transunion.

There are three major credit bureaus (Experiain, Transunion and Equifax). A creditor can check any/all of the bureaus at their discretion. A creditor can report your borrowing activity to none, one or all of the credit bureaus at their discretion.

You have the right to dispute information on your credit report that is incorrect. You cannot self-report your own borrowing activity, nor can you force a lender to report your activity.