WP_QUERY on serialised data

Hey Everyone,

I want to get posts from a custom post with a specific meta.
In the meta, there is a relation referred to as serialized data.

When I take a look through the wp_query documentation I can only find a way to filter on a single meta_value (or I overlook it).

When we unserialize the data we get the next:

( [0] => 2 )

The 2 is a user (the post has a relation with users).
How can I get the posts from WP_QUERY where the meta trainer is 2, without changing the serialised data.

Things I have tried:

                    'key' => 'trainer',
                    'value' => $currentUserId,
                    'compare' => 'IN'

But this doesn’t seem to work