At this moment it is not available for general customers, this is piloted on few selected customers of Microsoft and under review, soon the release will be available for everyone so watch out for further updates and news from Microsoft.
Note from Microsoft - "We are currently testing Microsoft 365 Copilot with 20 customers, including 8 in Fortune 500 enterprises. We will be expanding these previews to customers more broadly in the coming months and will share more on new controls for IT admins so that they can plan with confidence to enable Copilot across their organizations."
Read here - https://blogs.microsoft.com/blog/2023/03/16/introducing-microsoft-365-copilot-your-copilot-for-work/
Hope this helps.
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