When you unzip the file from Samsung you should see a bunch of files. You only need one, the AP_ TAR.MD5 file. It should be the largest file in there. When you load it into Odin, it could take a couple of minutes for the program to load and save it to memory. Wait until it has finished before moving on.
When the firmware has loaded, you should see the Start button ready to go. If it isn’t, unplug the phone from USB and reconnect it. Odin should say ‘Added!’ and you’re ready to go. If you cannot get Odin to recognize your phone, reboot your computer to make sure the Samsung Smart Switch driver was installed properly. Reinstall if you have issues.
Once you begin loading the firmware using Odin, do not touch your phone until it reboots. The process could take a few minutes and it may appear as if nothing is happening. Be patient and wait for that reboot. As it is a setup reboot, that will take longer too.
Replacing firmware is not something to do lightly. If you’re seeing Unknown Baseband Version errors, this is the only way I know of to fix it. Hope it goes well!