I changed BoundaryGeom to BoundaryGeog as seen below and now it throws the following:

UPDATE tl_2008_us_state

SET BoundaryGeog = GEOGRAPHY::STGeomFromWKB(BoundaryGeog.MakeValid().STAsBinary(), 4326)

WHERE NAME NOT IN('Massachusetts', 'New Mexico', 'Wyoming', 'Montana', 'Texas', 'North Carolina', 'Arizona', 'Tennessee', 'Utah')

Msg 6506, Level 16, State 10, Line 2

Could not find method 'MakeValid' for type 'Microsoft.SqlServer.Types.SqlGeography' in assembly 'Microsoft.SqlServer.Types'