simple circuit

Greetings everyone, I wanted to build a differential Op-Amp to help eliminate sensor voltage by subtract a preset baseline voltage (supply from voltage divider). After running simulation on LTSpice, it was found out that whenever I connected the voltage divider into the differential Op-Amp...

Found this simple circuit on youtube and I'd like to know the equation for how to vary R and C to change the flashing frequency. Also, how to increase the current through the led with 3.3 V battery as power source to maximize brightness.