Hello, @Parminder Sandhu !
Azure Reservations vs Capacity Reservation and IP/NSG
This is understandably an area of confusion so I'd like to start off by clarifying a couple of definitions:
These can be used together in combination to ensure that you both always have a set number of resources while also getting a discount for a bulk purchase and are sometimes described under the umbrella of Reserved VM Instances.
These reservations apply to your compute resource (the VM), and not other components like networking or storage although storage has its own reservation offering to save money which makes this a bit more confusing. When you create your VM, you would handle the public IP and Network Security Group (NSG) like you normally would--the reservation discount and capacity guarantee would apply to your compute/VM resource.
Applying free credits to your upgraded account
There are some limits to what your credits can be applied to and in this case, you are unable to use your credits towards reserved instances (thank you for the update, @Parminder Sandhu ). For other services, your remaining credit will be carried over for the full 30 days from when you signed up and that will apply to your charge. I would confirm what services qualify with sales/billing though, as the 2 day expiration means it would need to be processed immediately. All Azure accounts are able to open a billing support request in the Azure portal by going to Help + support > New support request > Billing and then complete the wizard.