Rahaman's suggestion is correct for necessary customizing for creating erp quotation from crm opportunity. Unfortunately, it is not what you need. I guess your(SINGH) scenario is that, you have existing crm opportunity in crm system and existing erp quotation in the erp system, but they are not linked.
It is easy for you to maintain docflow in crm but you will need to rfc call erp bapi to maintain docflow for erp quotation. I have this idea and hope it will give you some hint.
In standard ERP document in CRM logic, system maintain changes to an existing erp document in class cl_crm_intlay_erpil. Its method maintain_orders -> set_data -> if_crm_erp_lord_api~maintain
You may check if could help you maintain the docflow for your erp quotation. I have never tried it before and I am not sure if it works. But better than nothing. ^_&
Spencer