How do I even out clumps of feathers in a duvet?

[JaMmRocks]

That's it really, I have washed DS's duvet in a fit of efficiency but it's looking rather misshapen and odd.

Any tips?

Thanks

Put it on low heat in the tumble dryer with a tennis ball?

I have a north face feather filled jacket thing and it goes lumpy when washed. Above does get rid of the lumps (as advised by the shop...I was sceptical at first I have to admit)

I may have to take it to a launderette to do that, not sure I can squash it into our mini one

thank you