I wouldn't think SSMS natively supports doing this with a nice interface (e.g. a map). Maybe there's some add-on to allow this, or likely some 3rd party app.
If you're happy with doing it in SQL, try this:
UPDATE tableName SET geographyColumn = geography::Point(47.65100, -122.34900, 4326)
Derived from here.
Here are 4 more ways to do the same.