I am facing following issue: I want to calculate the α and β from the following probit model in R, which is defined as:

Probability = F(α + β sprdt ).

I can calculate probabilities for the entire dataset, the coeffcients etc. but I not know how to get the constant α and β.

The purpose is to determine the Spread in Excel that corresponds to a certain probability. E.g: Which Spread corresponds to 50% etc.

Thank you in advance!