The sulfuric acid used in car batteries is very dangerous to handle. If you can find a source, you may get lucky and replenish the battery with it. But, for me, I’d just consider this battery toast and simply replace it. I don’t have the equipment to handle battery acid safely and it is just not worth it to me considering the very dangerous potential for human and property damage.
Some of the shops I dealt with in my youth had batteries delivered dry, and had a special bladder with acid and a spill-proof nozzle designed to fill the battery cells and shut off the flow of acid before removing the nozzle. I haven’t seen anything like that in decades.