Helo, from the old bookkeeper of my office I recieved a backup.qbb file, but I don't know how to open it with 30-days trial

I'm happy to see you here in the Community, @yacky.

I got you covered with accessing the .QBB file that you received from your old bookkeeper. 

The .QBB file is a backup copy from a QuickBooks Desktop company file. That said, being able to access this directly in QuickBooks Online isn't available.

To achieve your goal, you'll need to restore that file on a Desktop version using our trial links. From there, you can export the data from the desktop version and import them into your QBO account. 

After downloading the trial version, you may restore the .QBB file by following the instructions found in this link: Restore a backup of your company file.

Once done, you can now move your file from QuickBooks Desktop to QuickBooks Online. Here's an article that will guide you throughout the process: Move your QuickBooks Desktop file to QuickBooks Online.

However, if you wish to open the file directly in QBO, you may consider checking a third-party application that supports this process. 

For your reference, I'm also adding here a link that contains details about the import limitation when converting your file from desktop to online: 

What to expect when you switch from QuickBooks Desktop to QuickBooks Online.

I'll be right here to help you if you have any other questions. Just let me know by leaving a reply below. Have a lovely day!

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@yacky 

Try open your data file on trial license as mentioned by BettyJaneB. If your data file is too old, you may need to convert in steps or purchase a 3rd party conversion service.