Open the cut settings editor for the C01 layer (double-click where it says C01):
In the Cut settings editor select the sub-layer tab (labelled ‘2 Line’) then the ‘-’ button:
This will delete the sub layer that makes this a ‘Multi’ layer. Click the ‘OK’ button.
This layer should now show as ‘Fill’ in the Cuts/Layers panel.
You might find the following docs page useful: