Welcome and thanks for posting your concern here in the Community. I'm here to provide some information about the process of changing a business entity in QuickBooks Desktop (QBDT).
You can create a new company file by copying the existing one. The copy will keep your accounts, lists (customers, vendors, items, etc.), templates, and preferences from the original company. Then use the Condense Data utility to remove all transactions.
To copy an existing QBDT company file, here's how:
1. Back up, then Restore your file.
2. Save the backup to a folder where you want to keep it, then rename the file.
3. Review the new company file.
After that, here's how to use the Condense Data utility:
1. On your new company file, go to File menu at the top, then pick Utilities on the drop-down.
2. Choose Condense Data, then select All Transactions.
3. Click Next, then follow the onscreen instructions to remove the transactions.
Once done, edit the entity type to S corp. Here's how:
1. Go to Company menu at the top, then pick My Company on the drop-down.
2. Click the Pencil icon, then choose Report Information on the left panel.
3. On the Income Tax Form Used drop-down, select Form 1120S ( S Corporation), then OK.