In this case the class teacher of your child is the first contact person. Parents, together with the school should consider which help can be offered, which measures are meaningful.
All general education schools in Hamburg offer free learning support for pupils (http://www.hamburg.de/bildungspaket-lernfoerderung/).
Parents also receive advice in the Regional Education and Counseling Centers (ReBBZ) http://www.hamburg.de/rebbz-regional/.
Pupils from families who get help for living can get benefits for learning support from the education and participation package (https://www.service.Hamburg.de/sixcms/detail.php?gsid=Hamburg128.c.46178.de)