Where do we input 1040-V payment on amended return?

Wife and I previously used filing status married filing separate in 2016. I received a refund. She had to pay $1500 using 1040-V. We are now amending our return and are using filing status married filing jointly. Where do we include the $1500 we originally paid towards her tax liability now that we are filing a 1040X amended return? Shouldn't we get credit for paying the $1500?