Hmmmm… assuming you’re logged in as administrator.. click on your hard drive once and press 🍎+ I together. You should see a long window… halfway down is the permissions for your hard drive/internal SSD… it’s a 2 position column… users on one side, permission on the other, click on the cog at the bottom to make changes( you may need to unlock it using your login name + password) , then lock it when you’re done, for the others, go to system prefs; then Users and Groups… and login as Administrator…
hope this helps..
John b