Replace Toilet Drain on Slab Fondation : Dig from under or Cut up from Top??

I have a slab that shifts,had it jacked up and toliet seems to have a kink init.I want to replace the whole pipe thing.Do i dig under the slab and in toit then go from there or take toliet off and cut concrete away all the way down to pipe? No it was not covered when got house jacked up. I was told you just dig down like 2 feet and under slab and whole thing is there? .The toliet is like 1 foot from outer wall i want to take off toilet after dig to pipe and take off replace tehn fill hole backin