Take the dogs for a walk together, keeping 10 feet between them so that they can’t greet each other or stare. Then, cross paths (still maintaining distance) and allow the dogs to smell where the other has walked. The idea is to acclimate them to each other’s presence without causing tension.
We do not recommend having them greet each other on leash nose to nose. This type of meeting can be very stressful for many dogs and can cause fear or reactions to being scared and defensive.