How to install a window ac in a room with improper window provision
Considering the circumstances you may be facing having to shift your premises back to the previously workable configuration!!

On another track you could consider using a different type of portable A/C unit altogether. There are available floor standing units that vent out through a large flexible hose to a window. There is typically an adjustable panel assembly that can be fitted to the window (see below). Note that there are also styles of these that use two of the flexible hoses.