It's good you're using QuickBooks and Harvest to manage your transactions. I'll be happy to guide you towards the right direction so you can get back back to doing what you love.
At the moment, there's a third-party app which allows you to seamlessly copy Harvest invoices to QuickBooks Online. This can be done by linking your accounts. To learn more about this app, I encourage you to check out this link here.
Otherwise, if you'd like to import your invoices manually through QBO here's a helpful article which shows you how: