Galacticare

Skins cost 100 Loamite in the Galactic Exchange, which you can get to by selecting the purple crystal beneath your money in the bottom left of the screen. Buy the Retro skin for a consultant you currently have working then select the consultant in your hospital and you'll see a skin selection screen where you can equip the Retro skin.

Getting a 5 star rating in mission 9 (this same chapter) grants a retro skin for the medibots. Once you achieve that rating you can just click on any medibot in the facility and switch its skin to the retro one. The achievement should pop immediately