Automorphisms of Higman graphs with $\mu=6$

We call a strongly regular graph with $v=\binom m2$ and $k=2(m-2)$ a Higman graph. In Higman graphs, the parameter $\mu$ takes values 4, 6, 7, and 8. We find possible orders of automorphisms of Higman graphs with $\mu =6$ and study the structure of fixed-point subgraphs of these automorphisms.