For example i have route /content-manager/relations/api::test.test/user and i want overwrite him, to return values which i need
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Hey Yurich, you can use this part of the documentation to discover how to overwrite API endpoints 
Controllers | Strapi Documentation
Yes, but this example you shared shows that I can overwrite the default /api/* requests
But I need to overwrite /content-manager/* requests
mb this could help
actually if you want to change the logic with relation of you content type “api:test.test” - you need to create new or change the core controller (GET, PUT, POST), where you can add you nessesary logic up to this docs Controllers | Strapi Documentation
Just decide at what point (on GET or PUT request for ex) you want to make changes to your collection type. Or there are some lifecycles to inject changes