altering a block that is embedded in a view I have a view and in the header of the view, I am rendering a custom block. The block is showing up just fine, however, I need to alter it and I cannot seem to figure this out. I have tried hook_preprocess_block, hook_block_view_alter and a couple others. I know the ID of my block but it isn't helping.

If I am embedding the block in the view and I want to alter the block, do I need to first alter the view and tell it to rerender the block? I am using drupal 8. Any help would be appreciated.
I assume you're displaying a block_content entity.

That is not actually rendered through the block system, it's an entity, so you need to implement hook_block_content_view() (see hook_ENTITY_TYPE_view() for documentation)