Hello Saurabh,
I assume you mean to make this a display only field?
Follow menu path as below:
Then choose object type RIH
The double click on 'UI Configuration" in the left hand dialog structure
Then change value for 'Read only" to 'True' and for 'Required' value as 'False' :
The result is that your number generation should still populate this value, but that it may not be manually input. You will have to test this and confirm
Regards
C