Dear Mansa,
Sorry I was confused with blocking material as reserving it.
For this you can amend the X-distr.chain status field of material master in "Sales: Sales Org1 " view.
If you wan to customize your own blocking reason then use below path in IMG menu Logistics - General > Material Master > Settings for Key Fields > Data Relevant to Sales and Distribution > Define Sales Statuses)
Regards
Ganesh