Step 1
Log in to your Shopify backend and go to Sales channels > Online store > Themes in the navigation on the left. Then click Customize on the right.
Step 2
Click on Theme actions > Edit code in the bottom left.
Step 3
Select the "theme.liquid" template from the layout folder and go to the bottom of the editor and paste your Userlike Widget code before the "</body>" tag. I Hit "Save" and your Shopify shop will be equipped with Userlike.
To avoid CSS conflicts with the chat client, we advise you not to use
iframe { !important } in your CSS. Better be more specific and exclude the Userlike chat client by using iframe:not(.userlike) { !important }.
read this article in English:
https://docs.userlike.com/setup/integration/shopify