Installation:

1. Download the included Python script file
2. Go into Blender. Click on "Edit" on the top left, then click "Preferences" from the drop-down
3. Go into the "Addons" tab, and click on the "Install" button on the upper right hand corner
4. On the file browser, navigate and select the Python script you just downloaded, and click on the blue "Install" button on the bottom right of the file browser window
5. Close the "Preferences" tab and while hovering over the viewport hit "N" to bring up the side panel, and you should see the "TexFind" category

How do I use this add-on?

Once you click on the TexFind category, you will see a panel. You will notice there's a directory path slot, and you can click on the folder icon to browse to the directory you're intending to insert (I highly recommend pasting the directory on the field if browsing to it doesn't display it, the add-on needs to know the full path to ensure there's no errors). The path you have just inserted is the path where the missing textures are (Example: Downloads folder on your computer) and all you have to do after that is click on replace missing textures for the invalid paths to be automatically updated on every corresponding image texture that has one. There is also a counter on the panel but you can reset it if you, for whatever reason, wanted to do so. To display the other 4 additional slots you need to click on the checkbox below the top directory path, which should display the rest and you should be able to fill those fields in as you need. Once you have finished specifying the directories just click on the replace missing textures button (if you have previously replaced textures in a directory you specified it won't conflict).

Note: You don't have to fill up all of the texture slots, you can just use what you need without a problem.