1 Kings 7:26 says:
2 Chronicles 4:5 says:
The two verses do not contradict. What we have here are two descriptions that are not mutually exclusive. If the container held 3000 baths at a certain point in time, then surely there was a point during its filling when it held 2000 baths. Neither 1 Kings 7:26 nor 2 Chronicles 4:5 purport to provide the upper limit of the capacity. When the historian of 1 Kings 7:26 observed the container, it held 2000 baths. When the historian of 2 Chronicles 4:5 observed the container, it held 3000 baths.