Once you’ve finished building your lead form, you’ll reach a page with your unique embed code on. Click on the simple embed code and copy it to your clipboard (CTRL+C for PC, and Command+C on Mac).
Now, login to your Shopify home and goto 'Online Store' in the left-hand navigation.
With the 'Online Store > Themes' page open you want to choose 'Customize' in the main area of the page.
With the 'Customizer' open, you must then choose to 'Add section' on the left-hand sidebar.
Then choose 'Custom content' under 'Advanced Layout' and press "Add".
Now with the Custom content container created, press 'Add content' under 'Content', and select 'Custom HTML'.
With the 'Custom HTML' container open, embed your lead form by pasting your embed code into the editor in text mode.
Once you’ve done this, save the changes by pressing 'Save' below. You should now see how your form will appear on the live site in the right-hand preview box.
If you want to make changes to your form, you can go back to the form customiser and make any necessary changes. Any changes you make will automatically update how your form looks on your website – there’s no need to re-embed the form.