ORA-01688: unable to extend table SCHEMA.TABLE_NAME partition P20091124 by 4096 in tablespace ABC_TBLSPACE

I know this
Error: ORA 1688
Text: unable to extend table %s.%s partition %s by %s in tablespace %s
---------------------------------------------------------------------------
Cause: Failed to allocate an extent for table segment in tablespace.
Action: Use ALTER TABLESPACE ADD DATAFILE statement to add one or more files
to the tablespace indicated.

This is ASM managed datafiles. How can I add more data files into this tablespace?

Now, this error pops up. When I'm trying to add datafile to the tblspace.
ORA-15041: diskgroup space exhausted

is the disc full on the server ?

@ Greert -

Its almost. But I still see around 200GB free space on the disk.

Thanks Geert. The disk was full and i'm cleaning up now.