create procedure with this query

In my opinion "check it therewill be duplicate if update delete the duplicate and insert in history table " should not be done as I almost bet the whole architecture including the history table was built like this just to prevent updates that would insert duplicate rows in the history which is obviously not allowed so...unless the whole thing is flawed and this is happening just because of poor design - I would check this first instead of potentially deleting valid useful historical data just so the updated can be done.

There is no history table 

Ok, in that case where is this "unique constraint (NATO.PK_NOC_ITEM_USRGRP) violated " coming from? Obviously the update is causing that PK violation.

There is already a unique constraint associated with the table.  Let the database do what it's designed to do and use the constraint to determine what's allowed and what isn't, not a separate query (and additional overhead) to see if an insert or update can be done.

BEGIN
  update noc_item_usrgrp
  set usr_usrgrp_code = '05'
  where usr_usrgrp_code = '17'
  and iug_seq = 1;
EXCEPTION
  WHEN DUP_VAL_ON_INDEX
  // handle the exception
  WHEN PK_NOC_ITEM_USRGRP
  // handle the exception

When the update is allowed, there's no additional overhead.  When the update violates the constraint, it is trapped and you can move data as needed.

Good Luck!
Kent

I think you need to better explain what you are trying to do.

Your question and comments don't seem to match up:

and insert in history table

and

There is no history table