[mgmine]

No picture. However, a three-piece panel set will not give any strength. They are used on simple doors like cabinets. Not being able to see what the problem is it's difficult to answer. But a garage door takes a lot of stress. If the structure is still intact and all you are doing is trying to hold a small panel or piece of glass in place then all you would need to do would be to cut an outside profile on a board to match the door and hold it in place from the inside. A piece of wood on the back or pocket hole screws from the back would do the job. If you are trying to replace a section of the door that runs the complete length then it would be time to get a new door.

 

[mgmine]

The pictures now are showing up but as Biagio said it's tough to figure out what you are trying to replace. How did you get just one piece out without taking the whole door apart? You said you cut a stile out if that is the case you won't be able to put a new one in unless the door is apart. You need room to be able to insert a dowel or tenon or anything like that.