Hi Narendran.
Not knowing the service order number, I selected an order that had the order status unique id value set to 840. I did not change this (nor execute any SQL scripts) but was able to search for the order in both the service order queue and the order locator.
From there, I opened the record and made the changes I needed to make to that order (it was incomplete as the last activity was not yet fulfilled). After completing all demands I was able to invoice it from the service order module with the NOW option.
This did not do the invoicing as it went to Need Audit status so presumably there is something in place (audit rule most likely) which did not allow it to invoice. So, going to the Audit Queue, I was able to find the order here was able to invoice it with the run/audit check.
Whether this is the best solution for your specific incident, I don't know but it does seem the status 840 (Rejected) does not prevent it from invoicing and it could proceed down the invoicing process presuming all the other requirements are fulfilled.