Following are some guidelines for formatting a Map chart’s Series Options. To display the Series Options for your map chart you can right-click on the outer portion of the map and select Format Chart Area in the right-click menu, or double-click on the outer portion of the map.
https://support.microsoft.com/en-us/office/format-a-map-chart-2c744937-a1cc-48f7-bc5e-776497343a29