Copy the image and use "Edit Transform Rotate" around the vanishing point then "Edit Transform Flip..." . Watch the perspective . If the mirrored surface is at 45 degrees from the vertical then the image will have rotated double that i.e. 90 degrees. You may have to use some content-aware fill as the mirror is likely to see an area outside of your original image.
See example below where I used some fill on the sky.
I hope that gets you started
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I see now
First straighten the verticals with edit Transform Perspective
Make a copy and mask it so the floor is transparent
Make another copy, of the original layer and Flip this copy vertically and drag it down so the bottom of the back door aligns. Now use Perspective Warp, in three sections (left right and centre) to keep centre unmoved whilst distorting the walls and floor edge.
Set this to around 53% opacity to let the original floor show through
You will have a little tidying to do round the floor join but hopefully that will get you started
Thank you very much.