Banneret's Training.

A banneret is a knight who inspires greatness in others by committing brave deeds in battle. The mere presence of one in a hamlet is enough to cause some orcs and bandits to seek easier prey. A lone banneret is a skilled warrior, but a banneret leading a band of allies can transform even the most poorly equipped militia into a ferocious war band.
A banneret prefers to lead through deeds, not words. As a banneret spearheads an attack, their actions can awaken reserves of courage and conviction in allies that they never suspected they had.

Level 3 Features:

Rallying Cry.

When you choose this archetype at 3rd level, you learn how to inspire your allies to fight on past their injuries.
When you use your Second Wind feature, you can choose up to three creatures within 60 feet of you that are allied with you. Each one regains hit points equal to your fighter level + your Charisma modifier, provided that the creature can see or hear you.

Royal Envoy.

Knights of high standing are expected to conduct themselves with grace.
At 3rd level, you gain proficiency in the Persuasion skill. If you are already proficient in it, you gain proficiency in one of the following skills of your choice: Animal Handling, Insight, Intimidation, or Performance.
Your proficiency bonus is doubled for any ability check you make that uses Persuasion. You receive this benefit regardless of the skill proficiency you gain from this feature.

Level 7 Feature:

Rousing Success.

At 7th level, when you score a critical hit on an attack roll or succeed on an ability check or saving throw, one creature of your choosing within 60 feet of you gains advantage on the next attack roll, ability check or saving throw they make in the next minute.

Level 10 Feature:

Inspiring Surge.

Starting at 10th level, when you use your Action Surge feature, you can choose one creature within 60 feet of you that is allied with you. That creature can immediately use its reaction to either make one weapon attack or move up to half of its speed without provoking opportunity attacks, provided that it can see or hear you.
Starting at 18th level, you can choose a number of additional allies equal to your Charisma modifier (minimum of 1 additional ally).

Level 15 Feature:

Bulwark.

Beginning at 15th level, you can extend the benefit of your Indomitable feature to your allies. When you decide to use Indomitable to reroll an Intelligence, a Wisdom, or a Charisma saving throw and you aren't incapacitated, any allies within 60 feet of you that also failed their saving throws against the same effect can reroll their saving throws and must use the new roll. An ally must be able to see or hear you to gain this benefit.

Level 18 Feature:

Inspiring Charge.

Starting at 18th level, you can choose two allies within 60 feet of you, rather than one.