Hello
In order to allow the calculation of the planned order basic dates for a specific number of days in the past, you can create an MRP group (transaction OPPR) and under the section "start in the past", you can defined how many days in the past are allowed. After that, the MRP group must be assigned to the material.
In order to allow the calculation of the production dates in the past, you can change the planned order scheduling parameters on transaction OPU5.
Best regards
Caetano Almeida