An Upload Dialog handler step should have automatically been added to the test when you recorded interacting with that dialog. If not, you can manually add one from the Dialogs button in the toolbar.
If that still doesn't work, it may be an issue with the title of the dialog. Notice it says "Open" and not "Choose File to Upload" as seen in a screen shot in the above link. In that case, you'll have to resort to handling the dialog in code. You will need to delete the Handle File Upload test step because implementing it in code will actually conflict with a non-coded dialog handler of the same type.
See the code sample below. Please note you will need to put in code the action that clicks the "Browse" button (or whatever the button is labeled that launches the Open File dialog).
// Initialize and activate a Handle FileUpload dialog handler
FileUploadDialog dlg =
// Click the button that causes the Open File dialog to launch
//(insert code here)
// Wait up to 10 seconds for the dialog to be handled, then deactivate the dialog handler
// to create and use a new one later in the test if needed.
The highlighted portion is where you indicate the custom title of the Upload dialog.
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