The local mobile phone sends a short message to the foreign mobile phone with prefix +86.

Actually, you don't need it. In your SMS center settings, you have set the SMS center number that uses the network, which is+86 * * * * * * * * * * * *. You don't need to re-enter every time you send a message, just enter the other party's mobile phone number, regardless of the local location.

You can open the message settings and enter the number in the message center number. You can ask your friends on the same network for the specific number, or you can ask your network service provider directly.