If the user has signed off, he cannot still have a lock on the record as all locks are released when a job ends.
DO a WRKOBJLCK to determine which job is locking the record.
Then you can determine where the real lock is.
If a user has just timed out and not signed off, he can still hold the lock.
You would need him to sign back on and then do a SIGNOFF.
If that is not possible, you cna do ENDJOB *IMMED for the job that has the record lock.