Steaming good. Wet, wrung-out tea towel, hot iron - let the steam
sizzle for a good few seconds - repeat as necessary until you've
lifted out all you can.

Works best on surface dings and compression type damage.

If it still needs filling, Brummer is the product used by most cabinet
makers:

http://www.axminster.co.uk/category-Fillers-206896.htm

You can also blend sawdust of the right colour with a glue like
cascamite to make up a matching filler.