If you were to try editing the locations, all you'll get is a point referencing the 8 missing municipalities, you won't get a new polygon out of Tableau if it isn't a part of the Open Streetmap collection to begin with. So your efforts wouldn't be fruitful. On your behalf I went looking for spatial (.shp) files for Kosovo or even Balklands and found very very few available resources. The one resource that I did find where I could see some possibilities was this site for the .shp file: GitHub - justinelliotmeyers/Kosovo_2018_Administrative_Boundaries
While the boundaries looked good, the files aren't useful as the gentleman didn't provide any municipality names to join to your data. The .shp files are simply the polygons with absolutely no attributes whatsoever. If you have some GIS software such as ArcGIS or QGIS you could potentially download his spatial files and correct the names. Beyond that I don't have any other useful options for you unless you can find some other spatial files online that might be available and then Tableau could bring that data in.
That being said, here's a site that I've found very useful over the years for available spatial (.shp) file datasets: https://freegisdata.rtwilson.com/ You can try searching for Kosovo administrative and/or municipal boundaries off that collection.
Your data would then need to be JOINED to something that matches in the .shp file such as municipality name in order to do what you're trying to build. Good luck! Thx, Don