You must copy the CA Certificate file (used in MySQL Server) in the storage phone (‘CACertificate.crt file’).

 Then navigate to Settings > Security> Credential Storage and select >Install from phone storage, select the file ‘CACertificate.crt’ and install it.

 You must verify that the CA Certificate file has been correctly installed. In order to verify Navigate to Settings > Security> Credential Storage >Trusted Credentials.

In this link you can see a video in which the process to be carried out is described: 

Mobile security settings video

Finally, Click on TLS option.