How to do image alt tags with php


I am using Wordpress 4.8.3 with rebound theme. But it does not support image alt tags from media lib. I have installed SEO optimized image plug in and it works fine with images in content area. But it does not work with logo and slider images. How should one configure it in Wordpress. I want to add html alt tag code, if so, how and where should I add it for logos and sliders?