Which command about the Spirit appears in 1 Thessalonians 5:19?

Answer: Do not quench the Spirit

1 Thess 5:19 says, "Do not extinguish the Spirit" (KJV: "Quench not the Spirit"). The command not to grieve the Spirit is in Ephesians 4:30.

“Do not extinguish the Spirit.”— 1 Thessalonians 5:19 (BSB)