How to set up voice over shortcuts

Hi everyone,

I've just set up a read aloud feature which is build into MacBooks, I've forgotten whether that's its formal name. But basically, if I press command + m together, a selection of keys which I selected in settings, it will read out highlighted text for me. Normally on YouTube and other apps if I press the space bar it pauses what is being read, however it doesn't do that with this feature, and the pause button on my MacBook Air is very small and hard to reach. Is there anyway I can change what the button for pause is on my keyboard when using this feature. Your help and explanations are greatly appreciated.

Many thanks.