The Map component is designed to use the OSM servers. I am not aware of any way to link the component directly to a file of OSM tiles you might have stored externally.
This is the Map components documentation. Nowhere is it described how to link a file of OSM tiles using the Map components.
Here is a way to use OSM without the Map component you might find useful.
Consider Verwendung vom (OpenAndroMaps) maps? I think they use the OSM tile model and their map system is used with offline map tiles.
If it helps:
Be aware, the Map component can access cached OpenStreetMap tiles offline ( they tiles have to have been previously accessed on line at least once in the area you wish to see a map.). An app made with the Map component caches map tiles automatically in your App Inventor Map that uses OSM. So it is possible, in some circumstances, to use the OSM tiles without accessing the OSM server.