Copy the "c592" folder (located in DLC folder) in your:

GAME DIR\mods\update\x64\dlcpacks

Then edit the "dlclist.xml" located in:

GAME DIR\mods\update\update.rpf\common\data
by adding:

<Item>dlcpacks:\c592\</Item>
After:
<Item>dlcpacks:/mpchristmas2018/</Item>

How to install Audio files :

1. Remember to Backup or use "Mods" Folder
2. Go to 
	D:\YOUR GTA ROOT\mods\update\x64\dlcpacks\mpbiker\dlc.rpf\x64\audio\sfx\dlc_biker\
3. Drag and drop the "oac" files.

Done.