is it possible to allow group role manage workflow permission

Kentico 7 is quite the old version. Kentico officially only gives you support 3 major versions back.

Documentation for Kentico 7 can be found using https://devnet.kentico.com/docs/7_0/devguide/index.html

In regards to workflow permissions: if you check https://devnet.kentico.com/docs/7_0/devguide/index.html?workflow_configuring_operators.htm, you'll see an short explanation how to add roles to the security settings of a workflow step. This should cover your case.

Thatns David te Kloese

But when we look at the roles in workflow step , it doesn't show roles defined for groups.

Ah, you mean the forum community groups, I'm not sure they were set up to be used for this type of permissions. Especially since it might be "public" users.

Only thing I can think of is create a global event handler that reacts when someone changes groups and assign a normal rule. But I'd be careful with setting permissions for those roles.