I need to work out a small dent in each of front and rear "bumpers" and cannot reach inside either with the parts on the car. Can anyone tell me how to remove them, please? It is a "Platinum" edition.

Front bar I removed several times, never removed the rear bar.
For front bar removal the steps are:
1. Remove the front plastic undertray - about twenty pesky scrivets hold it in place.
2. Remove all the scrivets across the top of the bar, about 6 or 8 of them IIRC. Don't forget the central one partly hidden by the bonnet latch. Includes removing the air intake snorkel, just two scrivets and it pulls off.
3. Remove three 10mm bolts each side which bolt the sides of the bar to the front quarter panels. Up from underneath, on each side one of them is a bit of a stretch to get at, you'll need a very long extender bar for your ratchet or else a very long screwdriver with 10mm socket fitting.
Tip for removing scrivets. They look like they will simply screw out, but only a few will, the rest just turn and turn and go nowhere fast. Grab two screw drivers, one with a very fine flat tip (eg a jeweller's screwdriver) and one with a small flat tip, and a set of needle-nosed pliers. Poke the screwdriver with a fine tip in between the edge of the 'screw' and the housing part of the scrivet and lever the screw out a bit. Then use the larger screw driver to lever it out further. Then use the needle nosed pliers to pull the screw all the way out. Then pull the scrivet housing out, by either levering a screwdriver under the edge, or use a small screwdriver stuck in the middle and lever away. If you're like most at least one of the scrivets will not come out without using brute force and destroying it, so it might pay to have a few spares on hand. About $6 each (I kid you not!) from the Mitsu stealership, or get some from the wreckers.