How do I access and use an AWS RDS reserved instance?
Reserved instances are a billing construct only.
If you buy a reserved instance for a m1.small in us-west-2a, all that means is that one of your on-demand RDS instances that's an m1.small in us-west-2a receives that lower hourly price (and incidentally, if you delete that instance and make a new one, the reservation's lower hourly rate just shifts onto the new instance). No instance is launched by reserving one.
Think of it as purchasing a licence for one of your existing instances you already have rather than creating a new instance.