Trying to make a homebrew set of armor for a campaign that I play in that adds a bonus to AC equal to the Charisma Modifier of the player. Does anyone know how to do this easily? Currently I've tried the following: Bonus -> Armor Class -> Ability Score (CHA).

And this did not work?

Wait for 20 mins save the blue save button twice

nope lol

Try Bonus->Armored Armor Class, then save the entire homebrew using the main [SAVE CHANGES] button under Basic Information or the system won’t pick up your changes automatically. After that it can take up to 20 minutes.

ill make sure to try that

That worked, thanks Iamsposta! I had to remember to attune the armor after equipping it, now it worked! 

I now have Vainglorious armor, from Griffon's Saddlebags.... ring mail armor that adds Cha bonus to armor class. Also changed their Cha boosting feature to adding a 1d6 bardic inspiration die when you roll a natural 20 for saving throw or attack roll. 

Here's the link, if interested:
https://www.dndbeyond.com/magic-items/6990256-vainglorious-armor

Happy to help.

Would you have any idea how to give a subclass the ability to use Constitution instead of Dexterity when calculating AC with Medium/ Light armor?

Nay with all armor:

• Modifier: Set->Subtype: Armored Armor Class->Ability Sclore:Con
• Set->AC Max Dex Armored Modifier->0