Catalysis of the reaction: S-adenosyl-L-methionine + 2-methyl-6-geranylgeranyl-1,4-benzoquinol = S-adenosyl-L-homocysteine + 2,3-dimethyl-6-geranylgeranyl-1,4-benzoquinol + H+.
2-methyl-6-geranylgeranyl-1,4-benzoquinol methyltransferase activity