Not so long ago, I had this problem. The problem is that you deleted that with the tool not eraser (from what I gather) If you used the eraser, or any other thing, the solution below works 100% of the time.
To put back the floor as wood tiles, you can use slabs
If you want the ground back, I believe that you can use the tools.
Furthermore, if you used the eraser on the ground, @Relyss please correct me if I am wrong here,but the result would be that it would erase the grass/soil tile. [If this is not possible, I belive that a glitch happened and the computer/ai/code assumed that that was what it wanted]