Hello. I have made footprints for a Arduino Mega 2560 R3 in PCB Editor. I want it mounted on the back of the board, but the only solution I know to put it on the other side of the board is to mirror the component. When I do this, the component mirror and drill holes are completely wrong. Therefore, I wondered if there is a solution for this, by turning it vertically or horizontally. I am open to other solutions too!
Not clear what your problem is. Placing a component on the bottom side in fact does mirror the footprint (as seen from the top side), in any PCB tool I know (quite a lot).
You have provided drill holes in component libray or on PCB.
If it is in PCB then you have to select "user defiend pick-up points" while flipping the component.
I would suggest to put drill holes in component itself if you have not done it.