Open the terminal…
and type: pkgman drop Haiku; pkgman drop HaikuPorts
choose yes and then type:
pkgman add https://eu.hpkg.haiku-os.org/haiku/master/$(getarch)/current
choose yes again and then finally type:
pkgman add https://eu.hpkg.haiku-os.org/haikuports/master/$(getarch)/current
No! Don’t do that 
“I downloaded the R1/beta1 version 64bit from 09/2018”
Don’t mix nightly and R1/beta1 haiku repositories.
If this is indeed R1/beta1:
pkgman add https://eu.hpkg.haiku-os.org/haiku/r1beta1/$(getarch)/current
pkgman add https://eu.hpkg.haiku-os.org/haikuports/master/$(getarch)/current
The package repositories that were configured during the installation of R1/beta1 should still work. Since they’re “stable” i’m definitley not breaking them any time soon
I downloaded the R1/beta1 version 64bit from 09/2018.
Take a look here: IMPORTANT: Repository changes
That only applies to nightly installations. It was also pre-R1/beta1.