The rate at which electromagnetic energy is radiated is given by Lamor's formula. What is the corresponding rate at which momentum is radiated and hence force to this?
where $p^\mu$ is the particle’s four-momentum and $\tau$ is the proper time along its worldline.
Larmor's formula isn't going to give you a force or momentum because it is a scalar equation telling you the total power radiated by an accelerated charge.
In order to know something about force/momentum you need to know the Poynting vector of the fields associated with the electromagnetic power, as a function of direction.