Do keep in mind that products uploaded via CSV are not synced with Modalyst, and you would need to update your store yourself.
Here's how you can download your CSV file with Modalyst:
1. Find products that you like and add them to your Import List
2. Click into your Import List
3. Click the checkbox to select all items and click "Export to CSV"
4. Export your list as a Generic CSV file
5. Check your e-mail to download the CSV file
Once you've downloaded the CSV file, you would need to re-arrange the columns to match the format set by your shopping cart software in order to upload all the products at once.