There is no really quick way to do it, it's a very slow and tedious process. First off there a few ways that I know of but i'm sure I don't know them all.
1st- If there is anything you can stand on that's your best bet. When you attempt to combo a Code it after about 5 hits it will use its attack but If you are on any (most) platform that is above the ground it wont hit you, thus keeping you safe. (wont work for 219 Survival)
2nd- Get Upper or Rush (II Would be preferable) and counter (II to speed it up). Upper is the better imo because you don't have to find the spot again and wont lure anymore Codes. When the Code wave comes stand on a diagonal in the corner and block, 1-3 Codes will be attacking you off the start but as long as you are blocking they shouldn't be able to hit you. You will notice that you will be receiving damage that shows up grey. Don't panic the extras will eventually run away if you try to get away then you will just lure more Codes leaving you with much less hp. Once you are down to 1 Code in front of you hold block and wait for you to counter but deal no damage as soon as you see this use upper cut. Hold block once more and repeat.
3rd- Almost Identical to the 2nd way but instead you only counter. Slower but it is easier to kill Kows will rush but you can't really use rush on Codes.
Tips-
The Codes will run away and you will have to try to lure them again so what I suggest is you tap the arrow key and hold block right after. Repate until it runs at you, hold block and it will either counter and deal damage or counter with no damage. If it does no damage then just keep holding block as I find the code will use another attack and deal damage to you.
Since the codes run away you can make it so they come right back. Once you have gotten rid of a few get the code between you and the wall and do the 2nd way. (USE AT OWN RISK, Code may turn and stomp dealing damage to you)
Don't trans, No trans can do much against Codes without dealing damage to yourself.
Hp is you best friend, If something seems too risking DON'T DO IT. You will need you HP for Xabs. (which I cannot solo)
Remember it takes much patience to get through the Code wave.
Hope this helped
Good Luck Have Fun.
(If you have any questions feel free to PM me or ask in game)