WP Smush Pro Trial - Cannot install dashboard

I cannot install this plugin to make use of the WP Pro Smush trial I just signed up for. It's just opening up a file to save on Firefox. Outside of installing themes within my WP site, I am pretty clueless.

Can someone please help me, since I just entered my card details to try the pro trial, but am unable to use it.

Be gentle with me - I am really not a pro with stuff like this. I just enjoy writing.