The start switch start the dryer but shuts itself when we release the button

Several different components could be preventing your dryer from continuing to run when the start button is released. The wiring diagram and other technical information for your dryer are shown in the image below. When the start (PTS or Push To Start) button is pushed, the PTS contact is closed and voltage is supplied to the drive motor. Start voltage is also sensed through the blue/black wire that is connected to the P1-5 Start Sense pin on the control board. When the control board senses the start voltage, it normally applies 48 volts DC voltage through the Pink/Black wire to the motor relay to hold the contact closed between the two blue wires attached to the motor relay that supplies normal run voltage to the drive motor. With the start button taped down, the motor continues to run since it gets voltage through the closed start button. Since the motor stops running when the start button is released, it indicates that you have one of these 3 failures:
Broken or disconnected Start Sense wire.

Failed electronic control board that is not sending the 48 volts DC voltage through the motor relay Failed motor relay. Wiring failure between the components.
Since the motor relay and the heater relay are both exactly the same part, you could unplug the dryer and switch the motor and heater relay to see if the dryer will stay running. If it does, then you just need to order and replace the bad relay.