This is a premium feature available with Astra Pro Addon plugin. To use these Pro features, you need to have the Astra theme along with the Astra Pro Addon installed on your website.
You can add WooCommerce Mini Cart in Header using the WooCommerce module available with Astra Pro. Please refer document, to begin with, WooCommerce module.
With Astra, you can add WooCommerce mini cart to the primary header with simple settings.
Make sure you have activated the WooCommerce plugin.
To find the setting, from WordPress dashboard navigate to Appearance > Customize > Header > Primary Menu > Last Menu in Item and choose WooCommerce.
It will display a WooCommerce cart icon at the end of the primary menu.
Like primary header, you can add a mini cart to Above Header and Below Header. Make sure Header Sections addon is activated.
To find the setting, from WordPress dashboard navigate to Appearance > Customize > Header > Above Header > Section ( 1/2 ) and choose WooCommerce.
Apart from the header, you might need to display a mini cart icon anywhere on the site. WooCommerce addon Provides WooCommerce Mini Cart Shortcode, that allows you to display the mini cart icon anywhere you want. Note that the shortcode will only work if you have Astra Pro installed and have WooCommerce addon activated from Astra Pro.
Refer to the article here for more information.