Force wide Tikz figure to move left

The package changepage can be your friend:

\begin{adjustwidth}{<leftmargin>}{<rightmargin>}

in one side documents and

\begin{adjustwidth*}{}{-8em}

(where -8em is width added to right margin of environment) for two side document. If you will provide MWE, I can show you an example of it use. In general you can do something like this:

\begin{figure}
\begin{adjustwidth*}{}{-8em} 
    \begin{tikzpicture}
    ...
    \end{tikzpicture}
\end{adjustwidth}
\end{figure}