From your Shopify admin, go to Online Store > Themes.
Find the theme that you want to edit and click Customize.
In the left-hand toolbar, click Theme settings.
Click Search suggestion.
Enable: turn on/off this feature.
Limit: adjust the maximum number of items per type (product, article, static page) per page.
Popup: add your text to display it as a small title above the search form.
Products block: add your text to display it as the product tab's title.
Article block: add your text to display it as the article tab's title.
Pages block: add your text to display it as the static page tab's title.
Please refer to this guide for more details.