I received a Roku HDMI extender but my TV is unable to detect Roku
Is your Roku working (showing an image/playing sound) without the HDMI Extender?
@StreamerUser yes it is
Try it in a different HDMI port.
Be warned that Roku does send out bad HDMI extenders (I received a flaky/bad one from them myself).
If its still problematic, contact Roku CS for a return/warranty service:
https://support.roku.com/contactus/returns-and-manage-orders
There's nothing special about the Roku HDMI extension, it's just a short (4 inches or so) HDMI cord with an HDMI plug at one end and an HDMI socket at the other. I use one several feet long to locate my Streaming Stick in an equipment closet on the other side of the wall from my TV. You may be able to find an HDMI extension locally or online and not have to wait for Roku to ship it to you.