This needs custom code, which means you need to modify Evolve+ Theme file. This is beyond our support scope.
I can only point you to the file and solution.
The previous_post_link and next_post_link are in navigation.php at line 14 and line 15
With reference to WordPress codex https://codex.wordpress.org/Function_Reference/previous_post_link and https://codex.wordpress.org/Function_Reference/next_post_link
You can set the variable $in_same_term to true.
Please hire a developer to assist you if you do not know how to set the variable.
And you will need to do your modification after every theme update.