The Article 29 Data Protection Working Group has published guidlines how and when it is mandatory to do a Data Protection Impact Assessment DPIA.
Data Protection and Privacy Impact Assessments
Data Protection Impact Assessment (DPIA) - Sprinto
Data Protection Impact Assessment (DPIA) Data Wheel.
DPIA GDPR Template xls Download
The DPIA process - step by step Data privacy and information
GDPR Data Protection Impact Assessment - Free Privacy Policy
GDPR: Initial Assessment & Data Protection Impact Assessment (DPIA
GDPR Data Protection Impact Assessment: 5-step methodology
GDPR Data Protection Impact Assessment - Free Privacy Policy