Automatic:
  > OpenIV
  > go to "mods/update/update.rpf/common/data
  > Drag and drop my "handling.meta" into OpenIV which replaces the game's existing "handling.meta"


Manual (If you have handling mods installed beforehand, such as Drive V, etc, and you do not want to hamper your existing mod): 
  > OpenIV
  > go to "mods/update/update.rpf/common/data
  > Go to "Manual" folder in my mod, open each .xml files, copy the whole code
  > In OpenIV, "handling.meta", right click, click on Edit, Search for the vehicle, replace the code with the one you copied
  > Repeat for all the vehicles, or only a few ones according to your desire

In case you need a tutorial video,
https://youtu.be/shh4U2gFTLM