Removing mould from grout

LTP grout stain remover or use a tungsten carbide blade to scrape out the grout (be careful you don’t scratch your tiles) and regrout it

I’d recommend HG Mould Spray, which is specifically designed for removing mould from tile grout. However, if you’ve already tried several products without success, the mould may have penetrated deep into the grout. In that case, the best long-term solution would be to remove the affected grout and regrout the area. It’s also important to improve ventilation to prevent the mould returning.