Do you want to add your own logo into your Navigation Bar?
Also in your Business Central Tenant:
Then follow these 9 Steps:
Navigate to your Microsoft 365 Admin Center
Jump into your "Settings" (if you don't see it, hit "Show all")
Open "Org. Settings"
Switch to "Organization profile"
Click on "Custom Themes"
On the right hand, open "Logos"
Upload a logo file under 10 kb or select an URL
Save a link (if mandatory) if you want to jump somewhere.
After that you need to set your theme to: "Organizational Theme"
Have Fun :-)