select disk to install windows

Forgive me if there is already an answer for what I am asking, I can't find it.
Is there any way to change the disk where the installation will be done?
I have a vps with a small 20GB disk in /dev/vda where a debian is installed and a 2TB /dev/vdb where I want to install windows but the script selects the small one and stops because of limited space.
I edited unattended.xml file and put install to disk 2 and the installation completed, but then could not boot because the partition wasn't active (I guess).
Any help is very appreciated.

Start by tracing the script's disk-selection logic for Windows installation and compare it with the edited unattended.xml. Reproduce the setup with /dev/vda and /dev/vdb, then determine how the selected disk is made bootable. Done means Windows installs to /dev/vdb and boots successfully without exhausting the 20GB disk.

Written by the indexing model from the issue text.