Are they a 3d print? Not familiar with the product.
If they're resin go and do the normal soap and water you would do for
https://tabletop-world.com/ products. If it's like Dwarven Forge you would do a basic soap wash the same and then rattlecan prime them.
However the Wizkids 3d dungeons were this cheap plastic... you could paint right over it with a spraypaint