Changing permissions for many boards in a project

@Mykola Manko - This is currently not possible, inside or outside of a project. There appears to be a few wish list idea posts requesting this functionality that you may want to upvote:

https://community.miro.com/search?q=manage%20boards&content_type%5B0%5D=ideation

You could also create your own Wish List post.

If you explain what you are trying to accomplish, there still may be options for you, e.g., project sharing settings can override board sharing permissions in some scenarios.