Hi @ramac1234,

Currently, there isn't an option to merge a company file in QuickBooks Online.

However, you can condense your company file if you're using a QuickBooks Desktop version. Please know that condensing your company file is irreversible. Thus said, you'll have to create a backup copy of your data first.

Once done, here's how you can condense your company file in QuickBooks Desktop:

1. Go to File.
2. Select Utilities.
3. Choose Condense Data.
4. Hit Next.
5. Click Begin Condense.

This way, you can now successfully condense your large QuickBooks file. In addition, I've also included our detailed guide in condensing a company file.

Lastly, you can check out this helpful article for your future reference: Resolve QuickBooks Desktop Performance Issues - Manage your Data File.

It'll be my pleasure to help if you have any other concerns. I'm always around ready to help.