Make sure you have Java 17 installed
Then create the start.bat file
Into it, paste:
"C:\Program Files\Java\jdk-17.0.9\bin\javaw.exe" -Xmx4G -Xms2048M -jar forge-14.23.5.2860.jar
pause
Keep the quotation marks and make sure the Java path is correct
Start the server with the bat file
Go to the official download site:
https://galacticraft.micdoodle8.com/mods/galacticraft/downloads
At bottom, select 1.12.2 and download all 3 mods
Replace all 3 mods with the current ones you are using