My pleasure. 

Although QuickBooks Online Plus doesn't handle inventory assemblies as discussed in your original post, the closest feature available is inventory bundling. This groups together multiple products/services that are sold in one single package: https://quickbooks.intuit.com/blog/whats-new/improving-your-efficiency-introducing-quickbooks-bundle....

For additional resources on setting up inventory tracking, cost accounting, and COGS, please feel free to check out the following articles: https://community.intuit.com/articles/1145670 and https://community.intuit.com/articles/1145499. 

I'm here if you have any further questions.