Avoid clients having to portforward to receive data

Hello there, my problem is I'm trying to make a client / server project.
Everything is fine so far.

This is how i was thinking it should work:

Client sends login-request to -> Server -> Server connects to MySQL db on localhost and checks if login was correct. Client & Server can now start communicating with each other and sending data between each other.

Here's my problem all though. If i want to send data to my clients they have to portforward that specific port my application is using, but i'd prefer having to go around this.

I've tested this and it works fine if i portforward the port on the server comp and get a friend to send data to me. So how do i go around this?

Thanks in advance ... Velreine