Improved Critical

[Jimlock]

Hello,

The level 3 fighter with "champion" archetype has the "Improved Critical" feature.

How to automate critical damage when "19" is obtained on attack roll ?

[LordEntrails]

See the Complete Package guides on how to create effects and automation for various class traits like Improved Critical.

Using the Site Search link above will also return you a bunch of similar threads that discuss and give you direct answers. Two that you should look at include;
Automating Improved Critical (Critical on 19 and 20) for Player characters in 5E (fantasygrounds.com)
FGU: "Improved critical" management/automation? (fantasygrounds.com)

[ddavison]

Click on the magnifying glass on the WEAPONS category on your Actions tab, and then you can change the critical threshold to 19 instead of 20. That would apply it to all weapon attacks. If you just want to apply it to a single attack, you can use effects as described in the linked posts.