There are many ways to rectify the mistakes, but it shall come through a structural consultant in written to ensure the structural consultant remains responsible for that act too.
following are the ways for rectifying same
1. Keep extra lapping by considering actual lapping below the beam bottom level or non lap area in column.
2. Do tack welding with cold welding rods as per the detailing given by structural consultant.
3. You can put the stirrups in that area as per confine zone spacing (again need to be approved by your structural consultant)
4. Do rework by cutting the existing bars to ensure you get lapping at correct level.