My volvo 740 was working before I changed the fuel filter. How do I relieve the pressure in the fuel line, or would it be something different?

 

well, that's unusual!

some prime the filter, i.e. fill it with gas prior to installing it but normally just cranking, providing you have a healthy pump and a battery, will take care of the problem. you can depress the relief valve at the filter or the one at the fuel rail to see how much fuel pressure there is and if there's air but that shouldn't be happening if the filter was installed correctly.