I needed a small holder for mounting an Arduino Nano and the one I found did not work, so I created a new one.
There is enough space to solder header pins in that mount on top of the Arduino Nano. (See attached photo.)
When the print is done and still hot/soft, try to fit the Arduino Nano in place, and gently bend the sides in/tighter or out/looser as needed.
I designed this in OpenSCAD.