Scrape on rear bumper

Someone has hit the rear bumper with (I think) a shopping trolley, creating a triangular flap about 1cm on each side in the silver-grey plastic coating and revealing the black plastic underneath. I was thinking of cutting a piece of duck tape to size, but I expect someone will have a better suggestion

(late 2015 'face-lift' model if that makes any difference)

I would get a paint repair set from the dealer.
You could also put one of these silly stickers over it, like " My other car is a Trabant "

Thanks jaapv. that sounds like a plan.

If you mean the silver rear valance , this is held on by a number of slide clips inside the bumper and can be replaced - although it costs around £180 from Mitsubishi but does come ready painted in silver. I had a a bit of damage on my rear valance so I took it off - reshaped the cut slightly with a hairdryer and then filled the slight dent that still existed with Flexifiller from Toolstation ( about £6 ) I then rubbed it down with 120 grit and eventually something like 600 grit wet and dry. Instead of painting it I took the valance to a local car vinyl wrapping business who wrapped the whole valance in matt silver and it looks pretty good. They charged about £25 and it only took about 20 minutes. Actually you could use any colour you wanted!
You can buy car wrap vinyl on line ( probably around £10 for a large enough bit and try and do it yourself if you wanted . My damage did go up to the black part of the bumper but I covered this with a stick on red reflector and matched it with one on the other side.

You can really only see any damage now if you looked for it very carefully.

Hope this could be useful to you