Make sure to first have SuperBLT, and CustomOST installed. Click the links in the dependency list.
Optional video tutorial for installing SuperBLT, BeardLib, and mod_overrides mods: https://youtu.be/rin_sjSJIkg
mods\CustomOSTTracks
should be placed in your customosttracks folder C:\Program Files (x86)\Steam\steamapps\common\PAYDAY 2\mods\CustomOSTTracks