Datafile Resize for Specific Tablespace

 DECLARE
  v_tablespace_name VARCHAR2(30) := 'YOUR_TABLESPACE_NAME'; -- Change to your tablespace name
  v_new_size        VARCHAR2(20) := '1024M'; -- New size for each datafile
BEGIN
  FOR rec IN (SELECT file_name
              FROM dba_data_files
              WHERE tablespace_name = v_tablespace_name) 
  LOOP
    EXECUTE IMMEDIATE 'ALTER DATABASE DATAFILE ''' || rec.file_name || ''' RESIZE ' || v_new_size;
  END LOOP;
END;
/