You either replace the chip, or use/build an HVSP (either a full on programmer, or more likely just the "fuse doctor" that sets fuses to make reset work again for reprogramming).
This is also a lesson - disabling reset makes your life much harder later on when (not if) you need to change the firmware. Try to avoid having to do that.
It sounds like you designed your own PCB. In that case, why didn't you use the ATmega328pb? It's supported in Arduino (via MiniCore), has 4 extra GPIO pins (A6/A7 are full fledged pins, not analog only, and it adds 2 more pins where a pair of power pins were), plus some other neat stuff like a second UART, I2C, and SPI interface. And it's got 2 more 16-bit timers too. The '328pb is basically what you'd get if you asked one of the experienced people around here what features they wished the '328p had.