How do I change the placeholder text in my header search box?

Edit the search component of your header:

1. Go to Settings → Appearance → Layout Settings, on the Header tab.
2. Scroll to Header Components and click Edit on the search row.
3. Change Placeholder. You can also set Submit Text for the button, Input Width, and Search with Category to show a category picker next to the box.
4. Click Save.

The component list belongs to your active header. If it is empty, activate a header first. If you use the Header Visual Builder, edit the search block inside the builder instead.