In Word, you can easily assign a keyboard shortcut (F key) to the Repeat/Redo function.
1. Go to Tools>Customize Keyboard...
2. Select "Edit" under Categories
3. Under Commands, scroll down to "EditRedoOrRepeat"
4. Place your cursor in the "Press new keyboard shortcut field" and press "F5" on your keyboard (F-keys 1 to 4 are controlled by MacOs). You can also press a combination of other keys such as Command x, Option x, etc.
5. Click "Assign," and you're done.