Return the full path of folder

Question

I am trying to return the full path of a directory that contain a specific name

I am trying to search location C:\test\
And trying to return the fullpathof a directory that contains AllTest

For example, if C:\test directory contains
Alltest.0.db folder

to return string filepath =  "C:\test\Alltest0.db"
Sometime, the folder name can be Alltest.1.0… or .. whatever..
How can I do this in C#?