According to the paper "A Thorough Study of State Leakage Mitigation in Quantum Computing with One-Time Pad" by Xu et la,[1]
Thermal Relaxation: This reset approach simply idles the qubit for a long time to allow decoherence to occur. Currently, quantum computers on most cloud platforms, such as IBM Quantum, are mainly using this approach.
reset instruction: The typical implementation of a “reset instruction” is based on a mid-circuit measurement followed by a conditional Pauli-X[...] IBM Quantum adopts this implementation.
So, thermal relaxation is used as a reset mechanism before running a new circuit, and measurement followed by a conditional-X is used for mid-circuit reset operations.