Have you tried this - select the record, then click on the edit icon (the one that looks like a pencil) in the top right corner? Once you are in edit mode, you should be able to change the field name or field type, and add more fields if you like.
Or if you have a template and wish to add or change any field within that template, you have to go to settings, templates, and select the template you wish to edit. You can even delete any template you are not using and don't wish to retain.
@John Were you able to try @JSeow's instructions to add fields to your data?
I would like to know how to edit fields in msecure. I am currently using the essentials but don't seem to be able to. Passwords plus had a custom field that would readily accommodate this.