unwanted new picture border

How was the border created.  If a simple frame like boarder. Crop it off.  If in a layer on an images within the document select the border pixels and delete them. If merged into the composite and its not the otter canvas edges that you can crop off select the boarders pixels and try content aware fill.  You did not give us any details of hoew it was added or the current state of your document  sounds like it may still in Photoshop and may be layered.