Where is the config file for this applet?

[jms1989]

I ask because every time my plasma build updates it loses it's config and I have to setup the entities and whatnot again.

[korapp]

It is managed by Plasma and stored in .config/plasma-org.kde.plasma.desktop-appletsrc, like all other plasmoids.
You can, however, use the built-in import/export feature.
Click ☰ in the Items section and then Export (to save your current items once) or enter an Auto backup path to always keep an up to date copy there. If you lose your items, simply use import to restore them.