Backdoor Conversion Earning Tax Question

I contributed $5.5K non deductible money directly into Roth IRA in 2018. In April 2019 before 4/15 I recharacterized $6.2K ($5.5K + $0.7K earnings) into Traditional, then immediately rollover to Roth.

I have two questions:

1) My understanding is earning is taxable. But should I calculate earning by the time of recharacterization or 2018 Year End?

2) I did not have a 2018 1099-R because the rechar and backdoor conversion happened in 2019. I owe that tax, how do I report it? Do I need to amend my 2018 1040? Or Do I submit a 8606?

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