Unless I’m missing something, there doesn’t seem to be an easy way to restore default settings in Kagi.
I am suggesting a button on the Advanced tab of Kagi settings to restore factory defaults.
Upon clicking this button, I would expect a menu with options to select which sets of options to reset (similar to how a reset in Orion on desktop works). Importantly, this would give the option to preserve things like custom bangs, lenses, assistants, redirects, site rankings, CSS snippets, and themes.
Basically, there should be a way to easily reset everything and also a way to easily reset just the basic general, search, and appearance settings.