Summary: The creation of heaven and earth and all things in them is evidenced by their existence.
All things that exist bear testimony of their creator by their existence
All things that exist bear testimony of their creator. How? By their existence.
For example, the existence of this stunt airplane:
The existence of this airplane serves as evidence of that airplane being a creation.
This is illustrated by the fact that we do not need a factory visit or a meeting with the aircraft company's owner to be persuaded. To see the airplane's existence is enough to have this fact established.
We do not know (or need to know):
The "how" and "who" are different matters.
Like one thing bears testimony of its creator by its existence, so do all other things
Like one thing bears testimony of its creator by its existence, so do all other things bear testimony of their creator.
For example, like the stunt airplane bears testimony, so does this bird (another flying object):
The existence of this bird serves as evidence of that bird being a creation.
Who that creator is and how the bird is made are different matters. Yet we have no doubt that it was brought into being.
That is, if we apply the same standard of evidence that we used for the airplane.