We can select a personal ringtone to the contacts stored on the OnePlus smartphone, so we can recognize who is calling from hearing the ring tone.

Besides the selection of the pre-installed ringtones, we can also define our own files, such as mp3s.

Android 10 | OxygenOS 10.0
Step 1:  Open the  Contacts app
Step 2:  Choose a  contact
Step 3:  Open the  menu
Step 4:  Tap on  Set ringtone
Step 5:  Enable or disable  Set   ringtone for each SIM card
Step 6:  Choose a  SIM card   (Dual SIM)
Step 7:  Choose a  ringtone
  1. Open the Contacts app
  2. Choose a contact
  3. Open the menu
  4. Tap on Set ringtone
  5. Enable or disable Set ringtone for each SIM card
  6. Choose a SIM card (Dual SIM)
  7. Choose a ringtone

OnePlus Instructions