LToolsPath is an option for LToolsLoadLibrary. It specifies the full path, to the LoopTools MathLink executable.
LToolsPath
LToolsLoadLibrary
The default value is FileNameJoin[{$FeynHelpersDirectory, "ExternalTools", "LoopTools", "LoopTools"}].
FileNameJoin[{$FeynHelpersDirectory, "ExternalTools", "LoopTools", "LoopTools"}]
Overview, LToolsLoadLibrary.