How to add Attunement slots

I'm homebrewing a rule to allow players to have the same number of attunement slots as their proficiency bonus. 

They are level 14 and currently have a +5 proficiency bonus. 

How do I configure dndbeyond.com to allow an extra 2 attuned items to their character sheets?

Thank you!

Modifier: Set->Subtype: Attunement->Fixed Value: 5

This seems like you're implying that an added homebrew race or class would be needed.

Also that if you want to limit it, but have it change as they level, you'd need to return and modify whenever their proficiency bonus increases.

Is that right? Or am I missing another place that this could be adjusted?

What about removing the attunement limit within DDB for ease, and just enforcing the limit manually.

edit: Found your homebrew feat, that seems way more manageable.

what modifier button are you talking about? how do I get there?

who's homebrew feat? what's it called?

Quote from Ramco >>

who's homebrew feat? what's it called?

 
Mine. This one: (https://www.dndbeyond.com/feats/265761-attuned)