Question

The invisible worm has found out thy bed of crimson joy.(turn into a complex sentence)

Answer 1

The invisible worm who has found out the bed of crimson joy.

Answer 2

Complex: The invisible worm has found out thy bed which is of crimson joy.

Here we have added the adjective clause: "which is of crimson joy."
This makes the sentence complex.
In the original sentence it is present as an adjective phrase: "of crimson joy".

Hope this helps. Thanks!