So this may be a bit advanced, but you could leverage the query string of a URL (e.g. yourwebsite.com/form/1234?field_123=value) in order to populate a default value when someone lands on a form. To do this, follow these steps:

You can also use this technique on a hidden field to store data from the source.

Please note this will only work on new submissions, it will be overwritten if they are editing their response.