Customizing a Theme

I just loaded the Connections plugin and I am trying to use it for a basic Phone Book. My entries are first name, last name, phone #1, phone #2, lot#. I would like to display to be one line; lot, first name, last name, phone #1 phone#2.

I thought I could edit the Default Entry Card 3.0 by?Steven A. Zahm template to accomplish this, but the customizer never loads. I am running WordPress at the latest level. Assuming I get this to work I am going to need to import 1500-2000 entries it is looks like I can purchase that option. I will also need to be able to print the entire directory.

Am I going in the right direction? My theme is Twenty Twenty-Three