How to highlight a threaded email in the new gmail interface?

Question

gmail

The interface has changed in Gmail and some things are incomprehensible.
For example, I had a correspondence of several letters (incoming and outgoing) from one addressee.
How can I highlight this chain?
In the old interface, it was enough to hover over the letter with the mouse cursor, and a navigation window appeared there, where there was an item to select a chain of letters.
And in the new one it is not clear how to do this?