How do I convert from cartesian ECEF coordinates to RA and Dec as seen from a specific earth location?

Question

I have the x,y,z positions of a gps satellite from its precise ephemerides and I am not sure how I can convert from these cartesian ECEF coordinates (WGS-84 G2139 IERS2010 frame specifically) to RA and Dec as seen from a specific earth location using something like astropy or skyfield?

I am not really sure what to try.