There are a few things you can try listed in
this topicMake sure your speech recognition profile has been trained at least three times, and only with the headset you're currently using (instructions for creating a new profile can be found
here).
If the input volume is generally too low even at its maximum setting, you may be able to enable a boost function in the software that came with your headset, or the properties for your device in the "Sound" applet (Ctrl-click the wrench icon on VoiceAttack's main window).
If you have a relatively recent NVIDIA graphics card, you may also be able to utilize RTX Voice, which will attempt to remove background noise (results may vary).