Can install simplemarket theme on market press

Hi, I admit I am only new to Wordpress but know enough to be able to install themes or plugins etc.
I have installed the Market Press plugin and it is activated with it now on the menu - store.
I downloaded the simple market theme into the themes directory and according to the instructions it should then show up as a theme in the drop down box under presentation but it isnt. One place I read with instructions says simply go appearance / themes and activate it. When I do that it overides the main buddyboss theme.
Ive been trying to fix this for hours now. Please can you tell me what Im doing wrong
thanks
Julie