If you have a knife [butterfly,m9,karambit, etc.] deselect it and equip the vanilla knifes for CT and T side.

You can choose 2 game modes:
- Workshop
- Offline with bots

Choose one.
In my tutorial i used "offline with bots".

If you are in the game you have to open the console and type in:

sv_cheats 1

After you done this write:

give weapon_knife_css;mp_drop_knife_enable 1;ent_fire weapon_knife addoutput "classname weapon_knifegg

The knife will be dropped under you or infront of you!