I'm working on a QCDSR paper which calculates mass of $B$ meson in the present of external magnetic field. the author works with Schwinger proper-time representation of Feynman propagator in momentum space. which is: $$S(k)=i\frac{\not{k}+m}{k^2-m^2}+(\frac{ceB}{m^2})[-(k_{\parallel}.\gamma_{\parallel}+m)\gamma^!\gamma^2\frac{m^2}{(k^2-m^2)^2}]+(\frac{ceB}{m^2})^2[-2ik^2_{\perp}(-\not{k}+m)\frac{m^4}{(k^2-m^2)^4}+2ik_{\perp}.\gamma_{\perp}\frac{m^4}{(k^2-m^2)^3}].$$
I want to recalculate of this paper, but in coordinate space. I know the Schwinger proper-time representation of Feynman diagram is:
$$DF(x_1-x_2)=-i\frac{1}{(2 \pi)^4}\int^{\infty}_0 ds s^2 e^{-is(m^2-i\epsilon)}e^{-isX^2/4}K_1(im\sqrt{s}).$$
I can't find any sources for Fourier transformation on Feynman propagator with power two or more of Denominator.
Can someone guide me on how to solve the equation?