First of all this game uses the in-game timer and success screen for actual times and verification. LiveSplit and the use of an auto-splitter is used primarily for tracking your current pace compared to other runs, seeing where you lost of gained time, sharing splits, sum of bests and a nice addition to progressing your personal best times.

To get started you'll want to download LiveSplit
You'll want to make a new folder and extract the contents - To launch the program doubleclick "Livesplit.exe"
Once you have LiveSplit you can begin setting up the auto-splitter.

Once opened, you'll get a small window with just a timer, you'll want to start by Right-clicking the timer and "Edit Splits". Under the "Game Name" Type or search for "Gunfire Reborn" and select it.
From here you can setup your category in the drop-down menu (These should pull from the categories on Speedrun.com. For additional category variables check additional info).
Underneath The categories you should see an Activate button, This is to activate the autosplitter (Created by Ero), which will automate the need to download/update the script manually. If you're wanting to automatically manage the script - Click activate and then Settings, Here you should see a list of check-boxes for places you want to enable auto-splitting. For this example we're going to leave it default which should have everything Checked except "Anxi desert Entrance" and "Duo Fjord Entrance". Once that all looks correct just click OK. If you choose to go the route of manually managing the script - This method no longer works for how the script is managed.
Now we're going to need to setup the splits that correspond to the autosplitter, For this we're going to need:
5 Splits for Longling Tomb
4 Splits for Anxi Desert
4 Splits for Duo Fjord 3 Splits for Hyperborean Jokul
The names of the splits don't matter for the functionality of autosplitting, these should be whatever you like them to be just make sure there's 13 Total.
Example:
Once that is setup click OK to exit out, Next we're going to change the timer to compare against in-game time by Right-clicking -> Compare against -> Game time. Make Sure to do this otherwise your timer is likely to show Real time instead of in-game time (Unless ofcourse you specifically want to use Real time)

Once that is done you should be setup and ready for runs. To check the timer is working correctly boot up a run and enter stage 1, The timer should auto-start - Also check that when pressing Inventory and the Escape menu the timer on LiveSplit pauses also, If not - Give your game and Livesplit a restart. Making sure to save your layout and splits before doing so. If the timer still doesn't behave correctly you might want to Right-click -> Edit Layout -> Layout Settings -> Then under Timer and Splits make sure the "Timing method" is either Current Timing method or Game time.
If you are playing multiplayer the timer should work perfectly fine as far as me and the community have tested, The method of interpreting the in-game time is looking directly to the value the game uses to display the timer, So any pause/change the game makes, the livesplit timer should also make

Big Shoutout to Ero for finding the Pointers and Writing the whole ASL script. If you have any issues with the script itself misbehaving contact Me, Cryorus or Ero. Either through Speedrun.com or Discord.