The idea of design V1 is automatic measurement when object is closed to sensor. MLX90614 sensor reading distance is 2~5mm. So, IR reflected sensor TCRT5000 is used to measure proximity distance. Circuit is simple. Analog out is connected to ESP32 pin 34 (ADC input).

Changed the code snip a little to measure if threshold ADC reading is changed. When the hand is closed to IR sensor and IR reflected sensor, temperature measurement is performed.

TCRT5000  Connection

Very rough test circuit for now :)