Filling holes on a polysurface

This is a beginner’s question, I know, because I’m a beginner.

Would any kind soul please tell me how to fill the crescent-shaped and triangular holes on this wooden deck?

Do you know how the holes were created?

Try Untrim

Not know what the starting surfaces were, I would probably just duplicate the edge of the crescent using “dupedge” and then draw a straight line across and join it. Then extrude it to the proper thickness. You can then “Booleanunion” and fillet / chamfer edges as necessary.
If it was truly just a hole I would use “Deletehole” but it looks like that probably wouldn’t work.