Inventory markup and service income

If you buy parts and stock them on hand, that is inventory.  And when you create inventory type items you set the sales price.  Use that item on a sales receipt or invoice, and the sale price will show (you can click in it and change it if you need to on the spot)

Labor charged for repairs would be a service type item posting to an income account.

If you are using external software you ought to look at whether it exports the necessary data to excel, if so there are third party apps that would import that transaction data for you.

I would suggest you call around and ask other local shops and see if they can recommend a QB consultant or QB accountant that can help you get it all set up.

Answers also depend on whether you are using QBO or desktop, and to be honest, questions about how to use QB are better placed on the support site than here.  https://community.intuit.com/