Reverting Custom Master Page change applied to all sub sites.

Hi,

Your quick help is appreciated.

I have a site collection with custom master page. But some sub sites were created with 2013 Team site template under the site collection.

So I had to make some change in the custom master page in site collection. I then went ahead and applied that change to all sub sites (by checking the boxes under Site settings (at site collection level) --> Look & Feel --> Master Pages --> Site Master Page & System Master Page). 

Now the sub sites are showing the custom master page with contents hidden. What should I do to revert back to old position where the site collection should have the custom master page (with the change I made) and sub sites going to the format it was having before.

Regards,

Suresh.