If you want to get started with some 3D design quick (and dirty) I can recommend tinkercad
Volkers father and volker designed this piece to fix a Playmobil toy truck:

and also a Playmobil helicopter:

If you want to get started with some 3D design quick (and dirty) I can recommend tinkercad
Volkers father and volker designed this piece to fix a Playmobil toy truck:
and also a Playmobil helicopter: