By using the number of individuals on your waiting list for a specific service as the 'demand' and by stating your targeted 'wait time' within the model as zero (as this is your current backlog you do not wish anyone to wait a further length of time), you have you can test how many additional appointments you would need to provide within your service to enable you to clear that backlog. This information can be translated into your resourcing plans around temporary or bank staffing to bring your service back on track.
In the example below, we think we can find an extra 5 appointments per week to absorb this waiting list, we want to try increasing that by 10 for modelling purposes and we have 50 people on our waiting list. We also know that within this service individuals normally see a practitioner for 6 appointments. As mentioned above, we have listed the wait time limit as 0 - we do not want our individuals on the waiting list to wait any longer.