To install this style of screen I typically put the top inside corner into the groove first and then the bottom inside corner next. Inside corner meaning the side that is directed towards the middle of the window and not the outside edge. Then I put in the outside top corner finishing with the bottom outside corner. Having a thin putty knife will make this easier. If you find your screen is built a little bit large and makes it difficult to put back in, put your putty knife between window frame and the screen frame allowing the screen to slide down the putty knife and drop into the channel. Sometimes if the screen seems too tall but the width is not that’s tight I will put in the top inside edge and then the top outside edge first. When I do this I have the screen down maybe 4 inches and then after I get the two top corners and I slide the screen up into the top groove. Then I put in the bottom inside corner finishing with the bottom outside corner using my putty knife to slide it into that channel.