When you create 2020 return, check the box "Transfer return data from year 2019" and select the tax return name (you could have multiple returns).

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To transfer your clients in batch to 2020, you can follow these steps:

1. Click on Settings in the bottom of the left panel;
2. In the popup, under TOOLS, click on Batch Actions (Transfer Prior Year Data);
3. Check the boxes for the returns you'd like to transfer; and
4. Press the Start transferring button in the bottom-right corner.