Why did the contractor pour the footings (and I guess the foundation wall) without allowing for the drain lines? I usually arrange with the contractor to set up the major drain and supply pipes BEFORE the concrete is poured. These pipes need to go THROUGH the foundation, and it is easy to incorporate the pipe runs through special forms, etc. before the concrete is poured. Once the foundation is in place the only way to get the pipes through it involve concrete demolition, sawing, and drilling. This is tedious and requires expensive equipment.
Thank goodness the slab hasn’t been poured yet, because that would require more demolition!
You need to discuss this with your contractor and plumber, because someone screwed up in the planning and execution of this job.
If you’re doing this job yourself, you have just learned an expensive lesson…