Encoding an SD card on Raspberry Pi 4B - newbie

Hi, I’m sorry to all the experienced people out here. I’m a newbie in data encryption, and I’ve been trying to find a thread/tutorial on how to deal with a similar problem like mine, but with no luck.
Some time ago, I bought a Zymkey 4i to protect my Raspberry Pi 4B from someone stealing the data. The data includes files and a few programs and interacting with each other, overwriting files, and changing system settings. In the future, the end customer will have physical access to it, and I need to protect it from reading the data. I’ve already set the Zymkey up and encrypted the root partition, but I do not know what to do next. I would appreciate any tips!