You may modify a Curator layout in Canva by following the steps below. We recommend using a full computer browser.

Choose the layout you wish to modify in the Customize Experience tab. Then download the PNG file for it:

Browse to the Canva website, then click 'Create Design' on the top right. A menu will open and select 'Edit Photo' towards the bottom. 

Browse to your layout .png file, then select 'Use in Design'

The modifiable file will now appear. On the left side are tools, such as 'Text' that you can use to apply custom verbiage and clipart to the layout file:

Once you have modified your layout, you can click on 'Share' at the top right, and select 'Download':

You should download your file with 'Transparent background' selected:

Once downloaded, you can now upload this layout back to the Curator website as a 'Custom Design':