How can i make my MLX90614ESF scan temperature after the MFRC522 scans the RFID tag?
It appears that you have simply concatenated the code from the RFID tag Sketch and the code from Temperature Sketch together.  This will not work as both programs contain identically named functions. Specifically &quot;setup()&quot; and &quot;loop()&quot;.  What you need to do is integrate the code for each &quot;setup()&quot; function into one &quot;setup()&quot; function.  Similarly, you need to do the same with the &quot;loop()&quot; functions.
Assuming you only want to scan the temperature after you have successfully recovered data from the RFID tag, place the Temperature Sketch loop code immediately before the delay in the RFID tag code.