The molarity of 30% H2O2 is (9.8 M ) , see this link https://www.homesciencetools.com/product/hydrogen-peroxide-30-ml/#:~:text=This%2030%20ml%20bottle%20of%20hydrogen%20peroxide%20is%20reagent%20grade,a%20molarity%20of%209.8%20M.

To prepare 43 mM you may use dilution equation M1 X V1 = M2 X V2

M2= 0.043 M

V2 you determine (e.g 1000 ml)

M1 = 9.8 M

V1 = ?

9.8 X V1 = 0.043 X 1000

calculate V1 and take the volume from the original bottle and complete to 1000 ml.