The Instagram widget in the theme is from Snapwidget. You have to register, but generating a widget is free.
Go to Snapwidget and create an account. Click on "Get a free widget" > "Create a free widget" > select "Instagram Grid" > "Click here to update username" > log in with your account.
Configure the settings like this:
- Thumbnail Size: 250
- Layout (Columns X Rows): 6 x 1
- Photo Padding: 25
- Hover Effect: None
- Sharing Buttons: No
- Responsive: Yes
Copy the generated code > go to your blog dashboard > Layout > open the "Instagram" widget from the After Footer widget area > paste the code inside.
Set up the widget on mobile like the demo
The demo has two widgets - one for desktop (6x1) and one for mobile (3x1, Photo Padding: 10), since using the 6x1 widget everywhere means the images on mobile will be very small.
To add a mobile widget, too, generate another Instagram widget and configure all the settings the same way, except for Layout (Columns X Rows) - it should be 3 x 1 instead of 6 x 1.
Copy the generated code > go to your blog dashboard > Layout > open the "Instagram" widget from the After Footer widget area > use the HTML below and insert the widgets between the classes:
<div class="instagram-outer">
<div class="instagram-inner">
<div class="instagram-desktop">
<!-- remove this line and add the desktop Instagram widget here -->
</div>
<div class="instagram-mobile">
<!-- remove this line and add the mobile Instagram widget here -->
</div>
</div>
</div>