how to store data file in Postgres

Hello Experts,
I created a database named "CIDR" using pg_default tablespace.  Now if I am moving the data/schemas/triggers/functions from Oracle into Postgres but the spacing is an issue.  From Oracle total datafile/tablespaces are 18G but in postgres where the pg_default tablespace has only 5G left.  I am asking for more disk spaces, SA is willing to give me another partition.  How do I move the CIDR database data file from where it is now to a new partition?
thank you. Bach-Nga

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