You can map your 1099-MISC vendor in QuickBooks Online (QBO) by opening the vendor's profile and enabling the Track payments for 1099 option. Here's a step-by-step guide:
Go to All apps.
In the Expenses & Bills, select Vendors.
Click the vendor(s), then select Edit button.
In the Additional info section, tick the Track payments for 1099 checkbox.
Hit Save.
To help you prepare 1099s in QBO, check out these articles: