You can run below commands to load the external table or add/remove files.
ALTER EXTERNAL TABLE [ IF EXISTS ] <name> REFRESH [ '<relative-path>' ]
ALTER EXTERNAL TABLE [ IF EXISTS ] <name> ADD FILES ( '<path>/[<filename>]' [ , [ '<path>/[<filename>'] ] )
ALTER EXTERNAL TABLE [ IF EXISTS ] <name> REMOVE FILES ( '<path>/[<filename>]' [ , [ '<path>/[<filename>]' ] )