All the above posts pretty much sum up my advice, but here is a little on working with epoxy putty. Depends of course on what brand you use, but I use milliput, and I find that it is too soft and sticky to work with for the first half hour or so. If you find the putty you are using is too soft at first, have a little patience. Apply it to the area and get it well seated and stuck on, then walk away for a little while, exactly how long will depend on the type of putty, experiment first with a small amount.
Once it has become a little more rubbery, then start to work with it, forming the creases and folds etc. Epoxy putty does respond well to water, so use this and a cheap paint brush to smooth the putty out before it is dry.
I use tooth picks that have been soaked in super glue, then sanded smooth, they work really well for pushing the epoxy around and formingthe creases, and they are cheap and disposable.
hope this helps
Phil