How do I use IINA as an alternative to QuickTime for .AVI video playback?

Download IINA from the official website. Find the downloaded .dmg file on your Mac. Double-click the .dmg to mount it as a virtual disk. You should see two items there: the application and a folder alias. Drag-and-drop the application onto this folder, to copy the application to the /Applications folder on your Mac. It is now installed.

• You can use the menus: IINA: File﹥Open﹥… to locate and open your media file.
• You can use drag-and-drop to move your media file icon to the application icon. For easy access, you can add the icon for IINA to the Dock. To do that, find the application in your /Applications folder, then drag-and-drop that app icon onto the Dock, in the wanted location between other apps there.
• You can change the default application for .avi files to your new media player application. Do a Get Info (⌘I) on your .avi file in Finder. In the new Information window, find the Open With section. Use the drop down menu to set a new application to handle this file by default. Click the Change All button to have this be applied for all .avi files on this Mac.