The ‘SwitchToDefault’ action compliments the ‘SwitchToIframe’ action as it allows you to exit the Iframe you have just entered. There is no information needed to use this action and it should be placed immediately after the action which interacts with the element within an Iframe.
Here is an example of the action used in a script:

You may encounter a series of Iframes within one section of a page, this is common on payment pages as each input field may be within an iframe. If this is the case it is important to switch in and out of each iframe individually as entering the first iframe will only allow input into the first field.
For more information on entering an iframe here is the documentation on ‘SwitchToIframe’ which is the first action in the process.