There is no builtin solution for the moment but looking at this help page, you can see that
Custom field names are an important identifier. Depending on the name you give your custom field, Bitwarden will attempt to auto-fill the custom field’s value for you. If you intend to auto-fill custom fields you should name your field based on an identifier from the webpage form. These names are searched for using the following criteria:
- HTML form element’s id attribute
- then the HTML form element’s name attribute
- then the HTML form element’s corresponding label value
- then the HTML form element’s aria-label attribute
- then the HTML form element’s placeholder attribute
If one of these matches is found, Bitwarden will auto-fill the custom field’s value for you.
To get one of these elements, you have to select the html element using the dev tools on your web browser. To do this, hit Ctrl/Cmd+Shift+C and point + click the form field you want to consider.
In the dev tools tab that opened, you can see the element and find an identifier such as the id, name, label, or something else.