Not able to change the AUTO_DEL_REC_OBJ value to ON I changed the value of AUTO_DEL_REC_OBJ to on as below in UAT and prod environment; in UAT it's done but in prod its current value is still showing OFF. What did I do wrong?
In UAT:
db2 update db cfg for CMNDB using AUTO_DEL_REC_OBJ ON

 Description                                   Parameter   Current Value              Delayed Value
 -------------------------------------------------------------------------------------------------------
Auto deletion of recovery objects    (AUTO_DEL_REC_OBJ) = ON                         ON

In Prod:
 Description                                   Parameter   Current Value              Delayed Value
 -------------------------------------------------------------------------------------------------------
Auto deletion of recovery objects    (AUTO_DEL_REC_OBJ) = OFF                        ON

Why has it changed in the UAT server but not in Prod?
You must connect to the database first to change some parameter online, if it's possible for this parameter:
db2 connect to CMNDB 
db2 update db cfg using AUTO_DEL_REC_OBJ ON
db2 get db cfg show detail | grep AUTO_DEL_REC_OBJ