Not sure what you mean by "second return" but you cannot efile a return twice. And you use the one account to complete the estimates either BEFORE you file or AFTER the return has been accepted. You didn't post what program you are even using ... online or downloaded .... so here is some general info :
Can TurboTax calculate next year's federal estimated taxes?
https://ttlc.intuit.com/replies/4242911
Can TurboTax calculate the estimated payments for next year's state taxes?
https://ttlc.intuit.com/replies/3301735
