Sometimes, accidents happen with your screen room. Somebody stumbles, a child throws a toy, or a pet gets a bit excited. A screen may get torn or a hole may be created. What can you do about it?
If you have a tear, you can try sewing together the loose pieces with a heavy thread that matches the colour of the mesh. Take care to ensure that the repair is done tightly, but not so tight as to cause distortions in the existing mesh. Some people use clear nail polish or something similar to seal the edges of the repair job in order to add some additional stability.
If you have a hole, you will want to even out the edges to form a square or rectangle as necessary. Using some tin snips (or even fingernail trimmers) may help get rid of the unwanted edges.
At this point, you can use heavy thread and create a set of rows (or columns) that match the existing mesh weave. This will take a little time and patience because you will tie one side and then the other. Make sure you have enough thread that matches the color of the mesh.
After your finish your rows or columns, then you do the same process for either the vertical or horizontal directions as necessary. You will want to weave the thread in order to provide more stability.
Seal the edges with nail polish or other similar coating.
If you have a patch of mesh that can be used as a replacement, cut it to match the shape of the hole. The patch should be a bit larger so that you can tie down the mesh at least twice per side (and then sealing the tied down areas).
If the hole or tear is too big, you will probably want to replace the entire screen. This involves removing the splines that keep the screen in and then replacing the screen. It's easier to use a little more screen that necessary, push the screen into the edges of the frame with the appropriate tool, then put the spline back in (or use replacement spline as necessary). Trim off the unneeded screen. Make sure the replacement screen is tightly in place.