Need help with Endokrinologie

Hello,

I was told that once you get an Indikationsschreiben you need to go to an Endokrinologie with it. Is this true? And if so, should I start searching now? I will get my schreiben in November/December or something like that.

Also, what should I write to the Endokrinologie? Can I even start looking for one before having my Indikationsschreiben? Do all Endokrinologie offer This treatment?

I'm based in Bonn/koln area if that helps any.

Thanks!