You can trim the edges of the HDMI and it will reduce this to 19mm (or so). It might fit through the conduit
But - no bends, or else very gradual ones
Push a fish tape through first and attach the HDMI cable so the fish tape connector passes under the wide side
Apply some washing up liquid to the sides of the plug and pull very slowly
It is fiddly. I have done it, but with difficulty
Is there no way to use a 25mm conduit?