QB Desktop provides the IIF feature for importing data but its capabilities are very limited.
You may have 2 options:
1, Purchase a third party conversion service.
2. Use the importer tool. It's a one-time $199 license and you can get $100 cash back for purchasing it through a partner. You will find templates for each type of transaction to import on their website.
https://get.transactionpro.com/qbd
