How do I enter my own amounts for custom recipe?

This is my first day trying to use Cronometer & I'm already stuck 🙃

I make a Coconut Kefir Chia Pudding - I use the full 1 L bottle, add my other ingredients & split into 12 jars, each jar is a single serving in my family.

Coconut Kefir only allows for a 3/4 cup entry ... our serving works out to only 1/3 cup ... how do I enter this ingredient into a custom recipe?