I’m a felon who was unaware of a gun in a vehicle that was not mine and got charged. The owner to the gun has sent in an affidavit owning ownership

The affidavit is good evidence to have. It is a strong affirmative link indicating him being in sole possession of the weapon. Possession means intentionally and knowingly having care, custody, control or management of the item. You can't accidently or unintentionally possess something. In situations where something like a weapon is found in an area of a vehicle that multiple people have access to, "affirmative links" are what the law considers, to determine whether either of the people (or both) were in legal possession. Affirmative links are things like who was driving the vehicle, who owned it, where the weapon was found, etc. The other party signing a sworn statement that it was theirs and theirs alone is also an affirmative link (in your favor).  But if your question is 'what do I do now?' Make sure your lawyer knows the law of possession real well. If he doesn't hire someone that does. Because if the DA can't be convinced to dismiss, the atrorney has to be able to fight your case at trial and win.