What formula relates electric field strength with kinetic energy and the magnetic field.?

To specifically answer your question, the main formula you need is:

Lorentz force F = q * v * B

with q charge of electron, v the velocity, and B intensity of magnetic field. This is a simplified equation based on your question, which assumes v and B are perpendicular, otherwise you need a sin(theta) factor, where theta is the angle between the velocity vector and the magnetic field.

You also need to know:
Kinetic energy = (1/2) * m * v * v
so v (velocity) = square root of ( 2 * Kinetic energy / m)

Use these constants for proper calculation (sorry for the formatting, but I I am limited in this text box on how to write an exponent as a superscript):
 
q = 1.6 x 10 at the power (-19) Coulomb
m = 9.11 x 10 at the power (-31) kg

In your case, just plug in the numbers to calculate F:
Kinetic energy = 1 MeV (this will give you the velocity v)
B = 2 mT