How to change image icon of service in front page? 2

Hello, in reference of the post How to change image icon of service in front page?, I'm going crazy ... I can't take the step: step 2:Go to=> Dashboard=> Appearance=> Page=> Edit Service page=> Set Featured Image I don't have the setting in my wordpress "Appearance=> Page=> Edit Service page=> Set Featured Image". I installed the Essential Content Types plugin I created the services, but nothing. I could ask to put the "Theme Instructions" link back online. You can help me I have been trying for two days without success