For those of you who don't know how to paint resources into your world, you need to open up Word (or any typing application) and save it as debug_enable.txt and then put it in the OxygenNotIncluded_Data folder. Make sure you don't write anything in the document. Assuming you didn't change the location when you downloaded Oxygen Not Included, the directory is as follows, C:\Program Files (x86)\Steam\steamapps\common\OxygenNotIncluded\OxygenNotIncluded_Data
Now to enable debug mode, press Shift+F4 to be able to build any building, even if you haven't unlocked it, and Backspace to go to the paint GUI. You can choose which element/compound to paint as well as the mass and temperature. By default, the option "Affect Buildings" is checked. I unchecked it after building a base so I could add in oxygen while I tried to figure out an oxygen production system. I went over the tiles into other rooms, as it would be less time consuming. It then replaced my tiles with oxygen.
Save a .txt file as debug_enable and put it in the OxygenNotIncluded_Data folder (Default directory: C:\Program Files (x86)\Steam\steamapps\common\OxygenNotIncluded\OxygenNotIncluded_Data ). Enable the paint GUI (Backspace) and uncheck "Affect Buildings." Select oxygen as the element and paint over tiles.