We have changed the Custom Form and Field page to be more consistent with other pages in Dash.
To create a new form or view existing forms, type in "custom forms" in the global search box. You can click on the pencil icon to edit an existing form or click the "+" to create a new form.
From the Custom Form page, on the left hand side, press the "Fields" option. This will display any existing fields you may have. You can press the pencil icon to edit and existing field or press the "+" symbol to create a new field.
For more detail on what custom forms can be used for and how to set these up, please check out this article here.