Open Infurnia and go to your design project.

In the Layersets panel on the left, click on the drop-down menu under "Active layer set."

Select the layer set that you want to rename to make it the active layer set.

Next, click on the settings icon (the gear icon) against the "Active layer set" drop-down menu.

Select "Rename" from the options.

In the popup that opens, you'll see a field where you can enter the desired name for the layer set.

Enter the new name for the layer set.

Click "Rename."