Start the app from the Add-ins tab on the Ribbon or with the command FixRefs. 

This is how JTB FixRefs find the missing reference file:

For example, when your old file path is "T:\A\B\C\D\E\Your Ref Filename", and you move your host drawing to a new folder "M:\New Location\Project 1", and you change the subfolder structure a little, then JTB FixRefs will check these file paths to see if it is available:

"M:\New Location\Project 1\A\B\C\D\E\Your Ref Filename"
"M:\New Location\Project 1\B\C\D\E\Your RefFilename"
"M:\New Location\Project 1\C\D\E\Your Ref Filename"
"M:\New Location\Project 1\D\E\Your Ref Filename"
"M:\New Location\Project 1\E\Your Ref Filename"
"M:\New Location\Project 1\Your Ref Filename"

In case all those file paths do not exist, you must enter the new file paths to the Fixed Paths column. Since it is a spreadsheet, it is easy to do using copy and paste tools

You can select the whole spreadsheet, copy and paste it to Excel. Then, in Excel, you can edit the paths using Excel's more powerful tools like Find and Replace, functions, etc. Finally, paste the data back properly to JTB FixRefs.

There are two tabs in the JTB FixRefs windows: the "Drawings" tab and the "External References" tab.

On each tab, you can see additional info of drawings and references objects: error when open drawing, error when saving drawing, drawing version, file not found, object is unreferenced, error when run fixing.

The installer that ran when you downloaded this app/plug-in from Autodesk App Store will start installing the app/plug-in. OR, simply double-click the downloaded installer to install the app/plugin. You may need to restart the Autodesk product to activate the app/plug-in.

To uninstall this plug-in, exit the Autodesk product if you are currently running it, simply rerun the installer, and select the "Uninstall" button. OR

On Windows 10 Version 1703 or later press Windows+I on the keyboard to access Settings or click the lower-left Start button on the desktop to expand Start Menu, and then select Settings in it. Click on Apps. On Windows 7/10 (older than Version 1703) click Control Panel > Programs > Programs and Features.

If your drawing is already open, the renamed object won't appear on the External References palettes until drawing is saved and reopened.