How to right override filecache.services.yml

Problem/Motivation

Hi, Filecache maintainers. First of all, thank you for this module.
I was able to enable igbinary serialization by editing the ‘filecache.services.yml’ file—which, of course, isn't the correct way—but I couldn't figure out how to create an override, even when I tried to replace it with my own “sites/default/services.yml” file and load it into settings.php after the filecache one.
How can I create an actual override?
I’d really appreciate any help you can offer.

Steps to reproduce

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes