How can I get rid of upper back fat fast?

Upper back fat is a sign of Metabolic Syndrome, and is something you should be concerned about beyond the way you look in a bra. You can't get rid of it fast. It increases your risk of heart disease, hormonal disorders, liver failure and assorted cancers. To get rid of it you have to change your diet, generally stop drinking alcohol or smoking, then transform a lot of your fat mass into muscle, and usually lose weight as well.

You can choose softer construction bras and lingerie that minimize the bulge factor though, and a clerk in any decent lingerie dept or store can help you out with that.

Than DON'T WEAR A BRA.

It can't be done "fast".

Better get educated about the proper ways to fit a bra.
Given the info, u have the wrong size bra on.
Upper back fat is nearly last fat to GO.