I have two list List A is Business Unit with column as Business Unit, Contact(People picker, Multiple),Manager(People picker, Multiple).
Another List name is RIM with column as Business Unit(Look Up from List A) Contact(People picker, Multiple),Manager(People picker, Multiple) and many more.
Now i want whenever List A Business Unit with field Contact(People picker, Multiple),Manager(People picker, Multiple) changes it should replicate the changes associated to that perticular business unit in RIM for the current item and also to taht item that has been already created.
I recommend creating a conditional workflow that will run when the required fields are changed on the list and then have a update item action in the workflow that will perform the update once the workflow start conditions equal true. You can set a condition for the workflow by opening the workflow in the workflow designer from the list ribbon and then click on Workflow Settings within the workflow designer.
If you have a unique field that is associated between both items on seperate lists, you could have a workflow that will trigger on a condition and in the workflow you would have another condition where if the unique field is equal, trigger a list workflow on the other list that runs on the specific item based on the unique field. I would look at the Set Condition and Start Workflow actions.