It looks like you have the "Reflective Floor Black" scene on. You can change the size and position of the floor if you like by editing the scene. Alternatively, you can just model the floor and apply whatever appearance you like to it so you are not entirely at the mercy of PV360.
Hi, many thanks for your answer, That was exactly what I wanted. How I strayed upon it in the first place I do not know! But thank you I am a little wiser now.