MLPPP - how to config public IP?

Hi I am tnew to MLPPP I have it running over two DSL connections, but the client requires that a public IP is assigned to the Multilink router rather than the private IP that appears to be there by default. Does anyone know what commands I can use to change the IP? Or where I can find the documentation on how to do so? Thanks in advance.

MLPPP has nothing to do with IP addressing