•⚡ Play the game fairly.
Getting reported for cheating/hacking can lower your Trust Factor.

• ⚡Get commended.
It seems you can retain a Green Trust Factor by getting commended. Remind other players to give commends if you feel like you deserved it.

• ⚡Don't be toxic.
CS:GO is taking steps against toxic players and besides degrading your Trust Factor, you could even receive a game ban from it even from Casual.

• ⚡Don't get kicked.
If you're getting kicked for griefing or other obvious reasons, great!
Otherwise, asking your teammates to kick you just so you could abandon a game without receiving a cool down will also degrade your Trust Factor.

•⚡Do some Over watch.
I haven't confirmed this but I heard doing some Overwatch cases legitimately can bring your Trust Factor back. I personally doubt it but feel free to try it out yourselves.

• ⚡Play non-competitive games.
Try playing Casual, Death match or other casual game modes until your Trust Factor goes Green again. Your Trust Factor can still be affect in casual game modes.