You are asking two different things. First, how to link to blocks in other notes, and also how to create an alias for a link.
Firstly, to create a link to a block in another file. Typing [[filename^ or [[^^ will bring up a modal you can type in to search for a specific block within other notes. If you want to link to a block within the same note, use a single chevron.
Secondly, after selecting the block you would like to link to, you can use the pipe character | after the link text but within the same [[]] to create an alias for the link.
When creating a link with an alias, it would be formatted as [[B.md|#2]]; this would show #2 as the link text inline but navigate to B.md when clicked. So in your case, you would have the link to the specific block rather than B.md.
Look at Link with aliases in the help guide on this topic for a better understanding.