The TRNKEYSTR is used to change the master key used to encrypt a key store.
The proper procedure should be:
Check the key store to see what master key was used to encrypt it.
Check the line
MEK version . . . . . . . . . . *CURRENT
If this line contains *OLD, you should run the TRNKEYSTR (if you do not do this and set a new master key, you will not be able to access this keystore)
Then create and set your Master Key
Then run the TRNKEYSTR