Replace the part it is leaking from.
You don't, You will need to either buy a new one from Cummins or an aftermarket one and figure out a way to plumb it in
First you have to identify the fluid that is leaking then locate the source of the leak before we can tell you how to repair it.
Factory location is on the back of the fuel filter housing. Service repair location is to move it to the fuel tank with a relocate kit.
My understanding is that it is not the oil filter housing leaking, that can be verified with a $2.00 replacement seal, and replaced by owner with a bit of ability, and tools, but it is more likely the timing chain cover that is leaking, with an estimated cost to repair of around $700, and that is mostly due to the shop labor for just getting to it.
check and see if the old rubber gaskit is stuck on the oil filter housing
Replace the gasket with a new one.
If it is where the filter meets up to the mount there actually is a gasket there. If it past the mount you may need to replace the filter housing.
The factory location for the lift pump is on the driver side of the block, below the fuel filter. The factory repair kit moves it to the fuel tank.
Any gasket or seal on the engine could be leaking. Have it checked by a trusted repair shop.
Some typical radiator repair jobs are leaking hoses, leaking radiators or loose connections.
Replace the leaking part
You will be better off replacing it that trying to repair it.