This feature is a long standing feature from State 270+. Recently this has been added to States 1-266 that made most of the old timer players who never played in new states confused including myself.
Players some players can access the Hero Training Area Via the Hero Precinct Building. There are two features that come with this. The Level Share and the Level Reset. This feature unlocks once your settlement level reaches level 16.
Once you add heroes to the Training Area, their levels cannot be upgraded but their ranks and skill levels can be upgraded manually ( assuming they are not General in Rank and their skill levels are not maxed to Level 5).
ONLY the heroes that are currently inside the settlement can be added to the Training Area and this restricts heroes that are either marching, attacking or gathering resources.
Level Share feature allows heroes to copy or match the Level of the Instructor with the lowest level. The 3 heroes with the highest Level will automatically become the instructors and these can be changed anytime. The initial slots for Hero Precinct Level 1-30 are 15 heroes and this will increase every time the Hero Precincnt reached Plasma. For every Plasma Level, more slots will be unlocked. ONLY the heroes inside the settlement can be added to the Training Area. Heroes marching, attacking, gathering resources or outside the settlement are restricted to enter.
Players can always decide on whatever heroes they want to set as instructors. The level share provides heroes the marching capacity that is equivalent to the level of the lowest instructor. Say the lowest instructor is Level 80 ( General), in means the heroes added to the training Area will have the same march capacity (13.47k).
LEVEL Reset is another feature that allows your hero levels to reset back to Level 1. Any hero with more than 0 XP ( it means more than level 1 can be reset. All combat manuals used will be returned to your backpack.
FREQUENTLY ASKED QUESTIONS:
HOW TO CHANGE THE INSTRUCTORS?
To change the default instructors, reset the current Instructors to level 1 via Level Reset. Choose 3 Heroes as preferred instructors and increase their levels to level 80.
MY COMBAT MANUALS ARE NOT ENOUGH TO MAX OUT MY HEROES ( FOR STATES 1-266)
For those wondering why they cannot max out their heroes after the feature implementation when they were all level 80, simply because the old requirements for combat manuals from the beginning of the game were different per rarity of heroes ( Blue and Purple Heroes before have less March capacity too). This is the reason why combat manuals are not enough to upgrade the heroes.
NEW REQUIREMENTS (ALL HERO RARITY)
WHAT HEROES TO USE AS INSTRUCTORS
If you are a maxed player with all heroes at Level 80, this feature does not matter whether you use it or not. If you are starting in a new State or short in combat manuals, you can make any GENERAL ranked heroes as your Instructor. This way the rest of the heroes you added in the Training area will adopt the march benefit.
For game newbies, you can set these three heroes as your Instructors provided they are of general rank. The reason why I choose them as Instructors is that they are the easiest the get to General Rank due to their rarity. Now, since you are just starting and only have limited slots to start (15 slots for Precinct 1-30), make Sarge, Ghost, and Rusty your Instructors and place the heroes you use for Attacks ( mainly the heroes you use for your First and Second marches) and Gatherers so they will temporarily adapt the level of your lowest level Instructors ( the one in blue).
You can increase the level of your heroes in the training area by running macro and burning your bread in the Explorer Trails.