The straps of your sandal have a default setting when you receive it. Since each foot is individual, you have to adjust the straps to your foot. This requires a bit of sensitivity at the beginning. Most likely you will have to readjust the straps after the first time you wear them. Once you have found a basic setting for your foot, the readjustment is quickly done.
It is best to proceed as follows:
The description shows how to extend the main band.
Shorten the heel strap (Fersenband) to form a loop.
Pull the main strap (Hauptband) forward to lengthen it.
Lay the straps flat on top of each other at the nodal-point so that they are not twisted.
For example, if you lengthen the main strap (Hauptband), the heel strap (Fersenband) will automatically shorten. As a rule, you will then have to lengthen the heel strap (Fersenband) at the nodal-point, heel strap (Fersenband) to instep strap (Ristband), as well.