Hi!
Unfortunately there is no easy modification for that – that feature requires a specific HTML layout as well as a custom script that would do the search.
For now, the best solution is probably to switch from the checkbox layout to a drop-down layout instead: https://i.imgur.com/ljWlfRt.png
In a future release, the following solution is going to be implemented: https://harvesthq.github.io/chosen/
It’s already under testing, I’m hoping to use this as soon as possible.