Use the SiteMind app
No code. The app puts the widget on your store and links it to your workspace.
Start from your dashboard
In Widget Studio, open the install panel and enter your store address, for example your-store.myshopify.com.
Approve the app
Shopify asks you to approve SiteMind for your store. Then sign in to SiteMind, or create an account, and confirm the link.
Turn on the app embed
In Shopify, open Online Store → Themes → Customize → App embeds and switch on SiteMind Chat. Save, and the widget is on your store.
Paste the snippet
Works on any plan, including the trial.
layout/theme.liquid
Copy your snippet
In your SiteMind dashboard, open Widget Studio and copy the embed code. It is one script tag with your widget key in it.
Open your theme code
From your Shopify admin, go to Online Store → Themes.
Edit code
On your current (published) theme, click the "…" menu, then Edit code.
Open theme.liquid
In the Layout folder on the left, open theme.liquid.
Paste and save
Paste the snippet on its own line, immediately before the closing </body> tag, then click Save.