How do you fill out the forms for a PTSD claim if you don’t have specific dates/incidents?

I separated 10 years ago. Did one year tour in Iraq, 2005. In 2017 a lot of things in my life fell apart and I was diagnosed with severe ptsd, depression, and anxiety. Anger and insomnia and all the good stuff. My therapist has been encouraging me to file a claim with the VA the past few years, so I finally did it. I have to fill out this form 21-0781 that is asking for the location of the incident, description of the incident, etc. the truth is that I don’t have a specific incident…. how do you explain death by 1,000 cuts? How am I supposed to fill out this form?