Best product to clean black mould from a gazebo cover

[KatyMac]

My commercial gazebo got put away wet after I was taken ill a few weeks ago

It's got some black marks I'm assuming mould

What can I use to clean them - it's about die fornrewaterproofing so I'll spend some time doing things properly

We used diluted Milton on our tent and then re-proofed it. Was okay.

Thanks I know where to buy Milton so.e of the things I googled looked scary