The codes on the Covid-19 Dashboard are the codes the DfE currently report on. If the code isn't on there, the DfE aren't reporting on this and isn't relevant to them.
You can't add codes to this dashboard. You can see a list of all of the current covid-related attendance codes here.
If you wish to report on Covid-19 marks for a period greater than 1 day or any codes not included in the Covid-19 dashboard, follow this article.