Templating a magic item

I'm working on a homebrew magic item that allows the wearer to choose any 3 of their ability scores and increase them by 2, however I can't seem to find a means to do so in the current magic item creator. I've tried creating a bonus modifier under "choose an ability score" but it yielded ineffective. Is there a way to create something like this with the tools currently available or would I have to tie it to a feat or something similar aswell?

“Modifier Type” = “Bonus”

“Modifier Subtype” = “Choose Ability Score” 

“Fixed Value” = “2” 

Did you put “2” in the “fixed value” field? That should work unless the character already has a 20 in that Ability Score.

The modifier added itself just fine. The issue is finding  where to choose the ability score on the actual character sheet. All of the other traits work fine, but there doesn't appear to be a prompt to let me choose the ability score. I'd think it's something similar to the drop down menu for feats and ability score improvements, but if that's incorrect I'd be glad to know where I can find that menu. Also I forgot to include this in the original post, but I'd like to do something similar with increasing the ability score maximums as well.