Use the Replace function.
Dim ReplaceIn as string = "Hello World"
Dim ToReplace as string = Space(1)
Dim ReplaceBy as string = "$"
Dim ReplacedString as string
ReplacedString= Replace(ReplaceIn, ToReplace,ReplaceBy)
ReplacedString should be equal to Hello$World
You could also look at
Regex[
^]