Quick and easy Keying question (pics inside)

How can I make the black night of this shot transparent??

basically trying to super impose this over a motorbike exhaust and am having great difficulty with my lack of experience with fusion - wand mask seems to not want to work for me... just makes the whole picture transparent.

Thanks for any help

You could just add it over the bg (merge with "Normal" mode and alpha gain at 0 or channel boolean and set to add)
Or you could try to create an alpha with a Luma keyer and then merge it over your BG