Unable to invoke BTT

I've used BTT for years and can't imagine my Mac without it. My 5 year old MBP suddenly started having kernel panics. After trying a lot of things I think I've got it stable now. However, although BTT is running, I can't invoke it using the standard CMD+space (or any command). I'm sorry for the really basic question, but I can't find where to set this up again - can someone advise please?