Importing a customisation file is very easy.
When you receive it, you can save it in any folder. Once you've done that, follow the instruction in the video or notes below.
Notes:
With Microsoft Word open, find an empty space in any tab, right-click that space and choose "Customize the tab" from the shortcut menu.
Alternatively, go to File, then Options and choose "Customize Ribbon" on the left-hand side of the dialog box.
Click the Import/Export button, which is just above the "OK" button, on the bottom-right of the dialog box.
Choose "Import customization file".
Find and select the file you've just opened. The file type is called "ExportedUI". Click Open.
A message appears asking you to confirm all existing customizations will be replaced. If this is your first time doing this, see below for more details. Otherwise, click "Yes".
The changes have been imported. Click OK to finish.
Should I replace my customizations?
If no changes have been made to your tabs, for example, you haven't added or removed any buttons to the Home or other tabs, or the Quick Access Toolbar, then answer Yes to this question. There are no changes to be replaced here.
If any changes have been made, including if you've switched on the Developer tab, please do the following:
Click "No".
Click on the "Import/Export" button, then choose "Export all customizations".
This will save your current customizations as a backup. Save the file in a folder of your choice.
Make a note of all customizations that are currently in your version of Microsoft Word.
Go back to the "Import/Export" button, click "Import customization file" (step 4 above) and carry on from there.
Sadly, it isn't known if there's an automatic way to combine customizations, so from your notes, restore any buttons and tabs manually.