Welcome to the Community space, @Adv Kelly. Let me share the steps on how you can seamlessly link your companies in QuickBooks.
You can export the lists and other data from the QuickBooks Online account to the other company. This way, you can seamlessly link the two companies.
Here's how:
Log in to your account.
Go to the Gear icon.
Choose Export data.
Toggle the data you want to export to On.
Click the Export to Excel button.
Once completed a .ZIP file will be downloaded containing the exported data. For export transactions, you'll want to use a third-party app. You can look for one online or in the App Center.