BLE peripheral_to_central

I am trying to send a n array of bytes from the BLE chip to the smartphone, AFTER I receive an array of bytes in the BLE chip from the smartphone, that is, my intended order of operation is as follows:

智能手机——祝福——> DA14580芯片——祝福——> smartphone

I have managed to do the first part (Smartphone --BLE--> DA14580 chip) but I am having trouble understanding how to do the second part

I am modifying the ble_app_peripheral sample program