RT’s file viewer does not have search capability. Instead, navigate to the folder containing in the right hand, tree view of your file system. You need to go to the lowest folder in the folder hierarchy, as RT will not show images in sub folders.
I do not know, what you did exactly. But maybe this helps:
In contrast to single clicks to see subfolders in a folder in the leftmost panel, you have to double-click the folder name in the this left panel to show the files in the central panel with the thumbnails for image selection. In the central panel you can then again double click to open an image in the editor.