[Solved] Get from 8th string character to last string character

You can just use

s2.Substring(7);

And it will take a substring starting from 7 index including 7th char.

Retrieves a substring from this instance. The substring starts at a
specified character position and continues to the end of the string.

https://msdn.microsoft.com/en-us/library/hxthx5h6(v=vs.110).aspx