Be sure that you press AND RELEASE the Google button on the remote BEFORE speaking (i.e. don’t hold the Google button down while you are speaking to it). You only need to press it once and release, and then begin speaking.
Note: To use Google Assistant, you must be logged in with a Google Account and your remote must be paired correctly with your Stream TV Box. If your voice is not being recognized, you may need to re-pair it. You can re-pair it by pressing the TiVo button, then selecting Menu (LEFT) / Settings / Remote Settings / Pair your remote with your box.