You are dealing with the following linear regression model
x1 = alpha + beta*x2
So, x2 is the predictor (independent variable), whereas x1 is the response variable (dependent variable).
You have already correctly computed the unstandardised regression coefficient, which is the correlation between the variables: -0.8333. you now want to compute the standardized coefficient, which is beta.
Beta = covariance (x1, x2) / variance(predictor)
Since x2 is the predictor:
Beta = covariance(x1,x2)/variance(x2)
Beta = -0.1/(0.2^2) = -2.5
This means that one unit increase in the standardized x2 is associated with 2.50 units decrease in x1.