How to alkalize moist fabric Here's some practical application of chemistry for ya.

In short:
I have a moist, hard-to-remove carpet in a car that's hard to get dry.
I treated it with an anti fungal agent containing 1/5 hydrogen peroxide supposed to kill the mold. Measured it - it's very acidic - a condition mold will like in the near future.

How do I alkalize the carpet without creating a mess? I'd like to do this w easily obtainable everyday substances.

(Explaining "mess": E.g. pouring calcium hydroxide on it would probably be a hard-to-remove mess?)

The long story for context:
I had a leak between the interior of my car and the engine compartment let rainwater moisten the carpet.
The leak was fixed, but in the past few months had really the wrong weather for getting it dry, silica absorber packs didn't help.
So, it started to mold.

To stop it, I bought an anti-mold agent fluid. I tested its pH value and it's off the scale acidic for my litmus paper.

Mold likes acidity, hence, as soon as the mold killing by oxidation wears off, the mold will like it even more, which is why I think I need to alkalize the carpet.
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.