1. After launching the game go to MODS from main menu.
2. At the bottom of your mods list there is a button that says ADD.
3. Paste into the field that appears after hitting the ADD button.
4. You may then have to back out of the menu or restart the game but you should then have a new mod preset matching the start of the code "B42-1 Valk's Easy Modlist 24-01-24"
5. Click the preset and then hit accept, it will stay enabled afterwards on further game launches.

If there isn't an ADD button then you haven't opted into the B42 beta.
1. Go to Zomboid in your steam library.
2. Right click, go to Properties, then Betas.
3. In the drop down select "unstable - UNSTABLE - BACKUP FIRST" and close the window.
4. The game will update to B42 then you can launch back in.