How do I exchange Noah points for my Hero?

If you already have the Noah points then go to the Tavern and select the 'Exchange' option at the top right. (Sometimes this comes up with a blank list as a bug but just tap Recruit and then Exchange again and you should see the list of available frags to buy with your points.

If you have excess frags for heroes you have already maxed you can exchange them for points in the Hero screen. Tap on Hero at the bottom and then select the 'Bag' option. Then you can recycle and spare frags into points.