How to change image on the post when shared offsite in php?

I have some job postings on my website, and for each Job Ad i want to share it on LinkedIn and Facebook. Up till here it works but there is a random image on that sharing. how can i change that?

I have used this

<a href="https://www.linkedin.com/sharing/share-offsite/?url=<?php echo (''.get_home_url().'/jobb/'.get_query_var('job_name'));?>" alt="linkedin"> Linked In </a>

but it shows this , see attched image.