Okay, I looked in other files and found answer to my question...
I created new file store.ts, added code @Samarium provided, then edited index.ts as follow:
Added import { engine } from "./store"
Then added "engine" to RpgModule
@RpgModule<RpgClient>({
engine,
sprite,
gui: [
titleGui,
loginGui
]
})
Is this the right approach?