I have Anaret 4.5/80mm that will cover 6x6 negative. One of the glass elements is moldy.

To be continued as I am still missing my tools. However in general you would use lens spanner and lens rubber stoppers to unscrew retaining rings, clean all glass elements with lens cleaning fluid and if moldy hydrogen peroxide. However if the lens is too moldy it might leave uneven surface even after cleaning. Such lens is nonrepairable.