If your child needs medical help from a specialist, your pediatrician may give you a referral to a specialist and also name you a specialist.
You can also look for a specialist yourself. Specialists in your area can be found in the local phonebook or Yellow Pages or the Internet. On the website of the Medical Association Hamburg https://www.aerztekammer-hamburg.org/arztsuche.html you can find all established specialists.
The appointmentservice center arranges appointments with medical specialists, if a referral exists: http://www.kvhh.net/kvhh/pages/index/p/1013
If you speak only a little German and therefore look for a doctor who speaks your language, the Kassenärztliche Vereinigung of the state in which you live, can help. The addresses and telephone numbers of the Kassenärztlichen Vereinigungen in the federal state in which you live can be found on the website: www.kbv.de/html/432.php.