How to alkalize moist fabric
If you really want to neutralize the acid of your mould removal product and don’t want to leave solid deposits, you can try a dilute aqueous solution of ammonia.

You can find typical solutions containing for example about 25 % ammonia (sometimes labelled “ammonium hydroxide”) in hardware stores. Such solutions are corrosive; they can cause severe skin burns and eye damage. You should dilute the solution to well below 5 %.

Ammonia is volatile; you will notice its characteristic pungent smell and you should thoroughly air the treated area. For the same reason, excess ammonia will evaporate and not leave solid deposits. However, it can form salts with the acid of your mould removal product and with carbon dioxide from the air. Such salts are water-soluble and, if necessary, they could be removed easily.

Ammonia is not corrosive to the metal parts of your car (ammonia is actually added to the feedwater of industrial boilers in order to keep the pH high and to reduce the risk of corrosion), except for open electrical contacts made of copper. However, you should test the ammonia solution on an unobtrusive spot to see whether it affects the colour of your carpet.