Hi Mart,

You have to use the Step Shaping command.

to access the command,  click right on the step nosing and select Step Shaping.

In “Regrouping” tick “none” and in the “Curves” use the drop down lists to add a 1/2 circle to left and right.

The final stair should look like this:

Note that in my example I’ll need to put a riser under the step to support it.

Hope this is helpful.

All the best,

Ness