In the secret browser that pops up after specifying the link in the browser automation action, hover over the element you want to manipulate using keyboard operations and click.
If there's no specific element to select, you can click anywhere on the page.

From the displayed options, select "Keyboard Operation".

Enter the action name. If not edited, it will default to "Perform Keyboard Operation".
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Select your preferred value from the available options and click "Add".

If the expected action is performed in the secret browser, your setup is complete.
The action will also be added to Yoom’s editing page.