Thanks for reaching out to the Community. I'd be happy to help with sharing more info on how the subscription works in QuickBooks.
At this time, you're allowed to have one subscription per account. If you have any questions about the subscription plans, feel free to contact our support team using this link here. You can also ask me any other questions. Please make sure you're as detailed as possible so we're both on the same page.
Just to clarifiy, there is none to download and install but QBO app if you are using QuickBooks Online. If you are using QuickBooks Desktop, you may download the installer file, running it and create/manage unlimited data file.