OK thought that is what you wanted to do.
If you are handy it can be done but my bet is it will be a PIA
First cut opening smaller than the clear plastic window you want to install
Cut the opening from bottom and the two sides only Thus giving you a flap of tent fab to roll upp to open window.
One would need a heavy gauge clear plastic sheet to make the window,
Cut hole smaller than the clear sheet size ,
Maybe use Velcro to secure it to the opening.
The Tent material flap could then also be secure with Black Velcro along it edges to seal when window is not in use.
Best way is sell that tent and buy one with window already.
You can see where I am going right.
