The basic answer is: you need to iterate through loop and check any element contains the specified string. So, let's say the code is:
foreach(string item in myList)
{
if(item.Contains(myString))
return item;
}
The equivalent, but terse, code is:
mylist.Where(x => x.Contains(myString)).FirstOrDefault();
Here, x is a parameter that acts like "item" in the above code.