LED blinking using LM358 operational amplifier
Increasing the capacitance is the obvious way to do what you want.

I think what @Andyaka is trying to say is that if you connect the negative terminal of an electrolytic capacitor to ground you won't have the problem of applying reverse voltages to it. However, electrolytic capacitors tend to be much more leaky than ceramic or other solid dielectric capacitors, so you may also need to reduce the value of R3.