Question: I have a concrete floor and I made two holes to bolt a 1/4"-thick steel plate. The problem is that the steel plates haven't been drilled yet.

How can I determine where the holes will be drilled in the steel plates so they match the holes in the concrete?
[![enter image description here](https://i.stack.imgur.com/1Kt5n.png)](https://i.stack.imgur.com/1Kt5n.png)

Answer: 
Do you really need to use the holes drilled in the concrete?

If not, pick another pair to be drilled far enough from the original ones. Make the hoes in the metal sheet first, put the sheet in position, secure it from movement and mark the spots or drill through the holes in the concrete.

Another point to be taken is how much the holes shall be coaxial. If the misfit can be in order of milimeters you can measure the position with a scale. If it must fit perfectly, two extra holes are a good tradeoff.
An alternative to Mark's idea would be to use plexiglass. Lay that down and mark either the center of the holes or the holes themselves. Drill through the plexiglass, make sure the holes are aligned properly, and then use that as a template to drill holes in the steel.

I would have added this as a comment under his answer but I don't have 50 reputation yet.