Login to your Shopify admin dashboard.
Click on Online Store and you'll see Theme section, here you'll see your current theme. If it's a Boundless theme proceed to step 3.
Click on Actions then Edit code.
Find customers/account.liquid under Templates section and then click on it.
You'll see few lines of code as shown below.
Go to Line no. 52 and paste the following code snippet.
your file should look like this.
Now, you're ready to use Super Rewards Custom Widget.