cannot change the robots.txt file on mulstisite subsites

I cannot change the robots.txt file - all sitemaps in the subsites robot.txt files point to my primary site of my multisite network... It also has Disallow ALL set and I need to change this on a per site basis...

I have installed a couple of plugins (Virtual Robots.txt and Robots.txt File) but neither one of them worked...

Pulling my hair out on this one and hoping someone can help me out here...

Thanks!