Merchants can now find the autocompletion setting in the checkout and accounts editor. It has been moved from its original location of Settings > Checkout.
To access the address autocompletion setting, to Settings > Checkout to the Configurations section. Click “Customize” next to the configuration you want to update
When you select “Use address autocompletion”, customers are enabled to enter their addresses faster and more accurately, accelerating the checkout experience.
Learn more about autocomplete in the Shopify Help Center