When doing risk controls, we lookup the total probability of a risk occurring (Ptotal) based off the occurrence probability (P1) and harm probability (P2) and the total risk probability matrix. In this case, we are not given P1 or P2 values, but only a Ptotal values.

In your organization, head to the advanced settings and find the total probability matrix configurations

(Project -> Settings -> Advanced -> Initial total probability matrix)

(Project -> Settings -> Advanced -> Residual total probability matrix)

For the total probability matrix, we can decide to obsolete one of the probability values by creating only one option for that value.

In the following examples, I decided to have my obsoleted value be 'N/A'.

Example 1: Obsoleting the P2 value, meaning that P1 is equivalent to Ptotal.

{
   "Low": {
      "N/A": "Low"
   },
   "Medium": {
      "N/A": "Medium"
   },
   "High": {
      "N/A": "High"
   }
}

Example 2: Obsoleting the P1 value, meaning that P2 is equivalent to Ptotal.

{
   "N/A": {
      "Low": "Low"
   },
   "N/A": {
      "Medium": "Medium"
   },
   "N/A": {
      "High": "High"
   }
}