To turn on archiving for an existing librarian master file you will need to reinitialize using the -OPT command.
Sample JCL below.
//JOBCARD
//*******************************************************************************************/
//* THIS SAMPLE JCL WILL USE AFOLIBR TO CHANGE THE */
//* INITIALIZATION SETTINGS OF A MASTER FILE. */
//* ALL OPTIONS REMAINED INTACT UNLESS ALTERED BY THIS JOB. */
//*******************************************************************************************/
//STEP1 EXEC PGM=AFOLIBR,PARM='NRJS,NJTA'
//OSJOB DD DUMMY
//SYSPRINT DD SYSOUT=*
//LIST DD SYSOUT=*
//INDEX DD SYSOUT=*
//MASTER DD DSN=YOUR.LIBRARIAN.MASTER.FILE,DISP=OLD
//SYSIN DD *
-OPT REINIT,ARC=5
/*
//
Note: Reinitializing a master file to support archiving does not automatically archive members. You must specify ARC on the -ADD or -SEL control statement for each member to archive.