If you want to access the data in instance B from the instance A. Then this is the query, you can edit your respective credential.
CREATE DATABASE LINK dblink_passport
CONNECT TO xxusernamexx IDENTIFIED BY xxpasswordxx
USING
'(DESCRIPTION=
(ADDRESS=
(PROTOCOL=TCP)
(HOST=xxipaddrxx / xxhostxx )
(PORT=xxportxx))
(CONNECT_DATA=
(SID=xxsidxx)))';
After executing this query access table
SELECT * FROM tablename@dblink_passport;
You can perform any operation DML, DDL, DQL