Add new field into "New Activity" box in Timeline

Hi GS community,

we use NXT and have just downloaded from the Sightline Vault the tool called Verified Outcomes.

The guide says: 

“The Outcome Category dropdown can be replaced with an Outcome Metric dropdown to provide a more detailed list of specific, measurable objectives; in this case, we recommend setting up a dependency so that the full Outcome Metric dropdown list is only available if Outcome Type = Quantitative was first selected.

Recommended: If using an Outcome Metric dropdown, it is recommended to also add a Metric Value numeric field so that the values of the Outcome Metric can be tracked over time”

So my idea is to add a new field called “Metric Value” (not sure if I’ll make it dependent on another, as this goes too far from my knowledge), but even if I want to keep things simple, I didn’t find a way or a document to add a new field here 

Can anyone please help me to implement this?

Thanks!

cheers