Here are the commands to remove/add weapons from a unit's inventory:

https://community.bistudio.com/wiki/removeWeapon
https://community.bistudio.com/wiki/removeAllWeapons

https://community.bistudio.com/wiki/addMagazine
https://community.bistudio.com/wiki/addWeapon

You will have to add an ; after every command.
If adding a new weapon to a unit's inventory, you will have to add a magazine for that weapon first in order for the weapon to be initially loaded.

Here is a site with information on what every weapon and ammo is called internally in the editor:
https://community.bistudio.com/wiki/ArmA:_Weapons

Here is an example of a correct command to clear a unit's inventory and replace it with other weapons. (Replace "Player" with "This" when you're replacing the inventory if you don't want to change the player's loadout)





First the unit's inventory is cleared, the initial loaded "Magazine" of Grenades is added, then the actual weapon and a spare magazine of ammo.



I'm not an expert in the editor myself but ask questions if you need any help.

Keep in mind the weapon selected for this example the "6G30" is not available in the original Combat Operations/Armed Assault, it was added in the Gold Edition. (So if you own this version of the game on Steam, it will work but otherwise it won't as it was added in the expansion.)