Hopefully, you set keep_wal_segments high enough that nothing has "expired" from the master, if this is the case and if you set up the slave so it can see those WAL segments, then your job is done. Just start the slave up and it will process those transactions from the WAL segments that weren't part of the pg_basebackup.
If, however, some of those WAL segments have disappeared off the master server, then you get to perform this exercise all over again, i.e., a new pg_basebackup.
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Jay