Go to your Event and then click "Galleries"
Next, click "Edit" next to the gallery you’d like make changes to.
Navigate to the "General" tab, and make sure you have "Display on Portfolio" toggled to on. This should then activate the drop down menu right below it, where you can select a Category, or enter in a Custom Category by clicking the edit "pencil" icon.
Select a Category or create a Custom Category, and click "Update Gallery" when you're done!
You'll then be able to see this online gallery appear on your portfolio under this new category!