First, read this tutorial:
https://www.facebook.com/groups/pentaxfotopublic/posts/3651475341686597/
In short, download the script files here for your camera model, namely, for K-1, K-1 II and K-3 III respectively:
https://mega.nz/folder/wWxWlJYb#reCBbvWHzcjRrnMzfpda3A
Follow the below steps:
1. Copy the unzipped files to the root directory of SD card and put the card in Slot 1 of the camera, with the original folder structure;
2. Turn off the camera and while pressing the "Menu" button, turning on the camera;
3. After seeing "Script - Enable", the camera can be turned off;
4. The four seasonal filters now become available after the camera is turned on again.
Btw, I have tried the above method for my K-3 III and the original K-1, both with the latest firmwares. It is found that only the K-3 III have had the filters successfully unleashed but I couldn't see the "Script - Enable" message with my K-1.