how can i change the materail availability date

Hi gurus,

We are using VA32 with schedule agreement.

When we create the new schedule line, material availability date calculating automatically.

Materail availability date = delivery date - route time (day)

For example;

delivery date                  : 28.10.2014

route day                        : 8 days

material availability date : 20.10.2014

if we need to change material availability date, we can not do it.

I don't want to change route, is there any possibility to change material availability date manually?

thanks.