Choose a block from the open block list, by its name: its configuration form opens in the dialog, where the block is added with "Add block".
Examples
When I choose "Syndicate" from the block list
When I choose "Search form" from the block list
When we choose "User login" from the block list
And I choose "Custom block" from the block list
When choose "Primary navigation" from the block list
Pattern
When(/^(I |we )*choose "([^"]*)" from the block list$/, …)
Part of @webship-js/backdrop-cms-steps (github.com/webship/backdrop-cms-steps), a step pack for Webship-js 2.0.x.