How can I set path for toolbox in add folder section?

When I try to set path the downloaded toolbox in Matlab, I can't see the downloaded toolbox's file or zip extension/file in the add folder. How can I fix my problem? I'm sure that I installed the toolbox. Even I look at the add-ons section I can see the installed written on the top of the toolbox. But why could not I find the toolbox file when I set?

[Jan]

Does this concern one of Matlab's toolboxes or did you download it from another author?

The dialog opened by the addfolder command, displays the contents of the current folder. If the folder, you have installed the new toolbox in is not the current folder, you cannot see it directly.

So please clarify: Where did you install which toolbox? We cannot guess this detail.