In some parts of the wilderness, I have a notoriety of 1, and in other parts I don't have notoriety at all. How can I reduce it?
The way that notoriety works in the frontier is as follows:
In most areas you are locked to one notoriety, this means you can't gain or lose in those areas.
In Concord and Lexington, you will be reduced to incognito mode if there is someone there you need to talk to. The same happens for homestead missions and huntsman missions.
If the game bugs and you gain notoriety, than you can lose it by moving zones or grabbing a wanted poster that spawns in Lexington (Left over, I'm sure, from an earlier version before the decision to force notoriety in the frontier)
You can't - you always have some base notoriety in a lot of places in the frontier.