Mould silcone bathtub help?

For the silicone, you need to scrape it clean and completely remove the old stuff with a putty knife before you reapply new silicone. You would have to do this even if there wasn't any mold on it. You cannot just silicone over old silicone, because the new stuff won't stick.

I would clean the grout with mold and mildew cleaner before I put new silicone, however. They make sprays that you'll spray on and leave, then with the condition that it's in, you should use a brush to clean it.

look on you tube of how to clean and caulk a tub or shower easy to learn just have to be willing to do the work

the black mold is caustic -- it must be killed and removed and then new caulk can be installed on a germ free surface .....