There are two ways you can do that.
(a) Either while framing the blog, you can tag the corresponding station. Tag button will be at the bottom, having a sign of a train.
(b) Or once you have already posted a blog, you will be able to see a button, called "Actions". You need to take your mouse on that and a drop-down option will come, where you will be able to see "Add Tag" option again.