what to do when a Theme uses a custom post type slug that conflicts with a plugin?

Disable the WordPress event plugin.

Use following code in functions.php to find your theme has events function.

if ( post_type_exists( 'events' ) ) {
       echo 'the Event post type exists';
}else{
       echo 'the Event post type does not exists';
}

1. If you find theme has events custom post type, find where your theme register the custom post type. Most probably it is functions.php. Check functions.php has register_post_type( 'events', $args ); . $args variable may be has different name. So find where is locating register_post_type( 'events', using IDE or pressing ctrl+f5.

2. If you found it in functions.php create a child theme. Just a google search, you can find how to create a child theme even you are not a WordPress developer. It is not hard.

3. Then copied functions.php file to child theme. Then remove the register_post_type( 'events', $args ); parts from it.