Leave a large selection of clues across their originating planet via some sort of basic, space born AI that will find a primitive planet spawning and have it place objects, scrolls. Written language all that kind of stuff eluding to the secrets of the Dyson sphere.

When they finally develop the industrial tools to detect and find a massive bunker deep under their planet. Where all clues indicate this holds the plans to the dyson sphere, they open it to find that it's just a fucking, Dyson Vacuum cleaner in the shape of a ball in honor of they Dyson Sphere's creation.