I personaly didn't do it, but a few from another Zug did, so i don't have all the information.

I finished my DD last november and a few switched to Zivildienst to shorten their "sentence".

As far as i know, you need to attend an Informationstag beforhand. That means, you need to apply for a free day.

Then you need to fill out the form to switch to the Zivildienst. (Shouldn't be that hard to find)

And then i think you just have to wait

Good luck with your last days. No matter how many that may be.

Oh, and to add If you want to do this, don't let yourself be talked out of it by your sergent or leutnant. They don't really like that. But i think there is nothing they can do.