For access to the GCC you will need to complete the pre-reqs listed in this article and follow the process https://learn.microsoft.com/en-us/office365/servicedescriptions/office-365-platform-service-description/office-365-us-government/microsoft-365-government-how-to-buy#microsoft-365-government-eligibility-and-validation
Also there has to be background checks on the resources that will manage the environment - more details here -https://learn.microsoft.com/en-us/office365/servicedescriptions/office-365-platform-service-description/office-365-us-government/gcc-high-and-dod
Hope this helps.
Please accept as answer and do a Thumbs-up to upvote this response if you are satisfied with the community help. Your upvote will be beneficial for the community users facing similar issues.