Need help Assigning 13000 MRUs to installations

Hi Experts,

I need help with assigning a list of MRUs to installations.

I have a list of 13000 MRUs and some details about them like their respective installation number to which they are assigned to and the BP, CA etc.

These are customer meter reading units which are assigned to the various installations,

Now I need to change the meter reading unit of these installation from a customer meter reading to a supplier meter reading unit.

For example MRU A1K1121(customer meter reading unit) is assigned to the installation 12345, therefore we need to change the MRU for the installation 12345 to A1L1121 which is a supplier meter reading unit.

We have to do the same thing for 13000 MRUs, how can I do this as fast as possible in one go?

Thanks a lot in advance!

Anshuman