First, copy the .jar of the version you want, (I'll be using 1.18.2 for an example).
Change the file extension of the copied .jar file to .zip, then extract.
Open the extracted folder named data, then follow this file path: data/minecraft/loot_tables,
Chose how/in what you want your item (for this example im going to be using the disc strad in a desert temple chest) to spawn.
Go to data/minecraft/loot_tables/chests/desert_pyramid.json,
Add the following to the .json file:
{
"type": "minecraft:item",
"weight": <weight of item generation chance>,
"functions": [
{
"function": "minecraft:set_count",
"count": {
"type": "minecraft:uniform",
"min": <Minimum amount that can spawn>,
"max": <Maximum amount that can spawn>
},
"add": false
}
],
"name": "<item tag ex. minecraft:music_disc_strad>"
}

Then save, re-zip the data folder with a pack.mcmeta and a pack.png, and ship it off to the world folder of your world/server <world/datapacks>, if you have any problems, go search up on google "How to change the loot tables of chests in Minecraft <your version here>".
You can also check out this article from the minecraft wiki, Have fun!