Processes in Microsoft 365 for setting up Office apps, redeeming product keys, and activating licenses.
A Fire HD 10 runs Fire OS, which is Amazon’s Android-based system. Microsoft 365 apps on tablets are the mobile versions, not the full Windows/Mac desktop apps. So even with a Microsoft 365 subscription, you may still be limited compared with Word/Excel/PowerPoint on a PC or Mac.
Your realistic option is
Open the web browser and go to:
https://www.office.com > Apps
This gives you Word, Excel, PowerPoint, Outlook, OneDrive, etc. in the web versions. This is probably the best option on a Fire tablet due to OS limitation.