First, it looks like most w3w locators / converters will require a w3w api key. Once that's taken care of, I'd take a look at these sites that explains how to add the locator to ArcGIS Online and ArcGIS Pro:
https://developer.what3words.com/tutorial/how-to-setup-the-what3words-locator-for-arcgis-online#addi...
https://developer.what3words.com/tutorial/using-the-what3words-arcgis-locator-in-arcgis-pro#get-an-a...
Once you have the locator in your project, you could use one of the Geocoding geoprocessing tools to convert them if you have them in a table.
If you're comfortable with Python, you could also perform this process using the geocoder module, although you would need to install it since it's not included in ArcGIS Pro's default environment, so it may be less trouble to just use the Geoprocessing tools.
https://geocoder.readthedocs.io/providers/What3Words.html
