Prerequisite: Your site must be verified with Google Search Console. If it is not then please do that first by following How to verify site with Google Search Console

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Step 1:

• Sign into your Google Search Console (formerly known as Webmaster Tools): https://www.google.com/webmasters

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Step 2:

• Click on a property to edit

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Step 3:

• Scroll down to Current Status section
• Click Sitemaps

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Step 4:

• Click ADD/TEST SITEMAP

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Step 5:

• Enter sitemap_index.xml
• Click Submit

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Also recommend:
How to add Google Analytics
How to get a Google Map/API Key
How to use Google My Business
How to create structured data markup