The footer is added via PHP as a Divi Library Layout.
Navigate to Divi > Divi Library in the WordPress menu.
In the library there is a layout under the category Global Items called Global Footer.
Open each of the modules and edit as you see fit or add new ones. These changes will be reflected across your entire site.
To change the Instagram feed to your own, first visit https://snapwidget.com and create a new slider widget, the settings do not matter as we just need your unique code.
Once you have finished creating the widget, click Get Widget and you will be presented with some code similar to the following:
<!-- SnapWidget -->
<iframe src="https://snapwidget.com/embed/123456" class="snapwidget-widget" allowTransparency="true" frameborder="0" scrolling="no" style="border:none; overflow:hidden; width:1080px; height:125px"></iframe>
Make a note of the number you see after the snap widget embed url (shown here in green), you can then exit Snap Widget. Do not copy the entire code as it has been edited for Ophelia.
Next, open up the Code Module you see in the Instagram section of the Global Footer Layout.
Change the number that is appended to the snap widget embed url to the one you copied from Snap Widget and save.
After refreshing your page your own Instagram images should now be displayed in the feed.