Yes what AL82 says is correct. Healing a gangster with the 'Heal' Ability or an health consumable (Doctors Bag and above if I recall correctly) will remove STD's from a Gangster. The reason why we say that only Doctors can heal is because only the Doctor Profession (and some Bosses) has the 'Heal' ability in their talent tree (as well as Remedy and Miracle Cure) which are healing abilities and not health consumables. Information regarding the use of the Radial Menu is given during the tutorial, and when we added the various healing options to it it was part of the update notes. There's an interesting discussion that could be had regarding the amount of experimentation game developers can expect of their players, though that is probably for another time.
There are several Sub Forums, General Discussion is for question like these 'How do I do X?' or 'Is Y a bug or a feature?' Technical Support is for more hardware related issues, the Game not booting, odd interactions between pieces of hardware and such. Bug Reports are for things you are almost certain are a bug and want us to know about so we can fix it. With my response I only intended to clarify the different roles one might see on the forums and make clear that the sassy, passive aggressive tone is generally frowned upon, it was not my intention to come across as combative. I didn't go further into your question as I assumed that you had already tried what AL82 suggested and verified that it worked, that was my mistake.