Valve does not publish the exact formula, but over the years, the community has verified several methods to organically raise your Trust Factor and get back into high-quality lobbies.
The Fixes:
Play Uninterrupted: Play matches from start to finish without disconnecting or doing team damage.
Overwatch / Commends: Being a positive force in Voice Commms and receiving in-game "Commends" (Friendly, Teacher, Leader) from teammates passively boosts your standing.
Account Health: Link a phone number to your Steam account (Prime Status), enable Steam Guard Mobile Authenticator, and engage with the Steam community positively (leaving legitimate comments, playing other games).