If I am getting a lease transferred to me, what happens to the security deposit?

A tenant’s lease is being transferred over to me with 6 months left. How should I split the return of their security deposit since I am taking over someone’s lease? Should I refund all of it to them, or should I give them half since they are leaving mid-lease and then return the other half when the lease ends? The landlord is keeping their portion of the security deposit until the lease ends in 6 months. This is my first time doing this so I am not sure where to start.