Unfortunately the source of this information is not very scientific (Daily Mail), but one described case seems to partially base on a credible source (see PDF link on the page below):
onlinelibrary.wiley.com/doi...
Don't try this at home! Wait for thousands of more reports showing miraculously cured people first (logic says we should see a lot of them, with COVID-19 pandemic so widespread) - and treat it it as some kind of "this one in a million lottery winner case".
Daily Mail article below:
dailymail.co.uk/health/arti...
Did catching Covid-19 help these patients fight cancer? One saw his tumours vanish, another went into remission. Now doctors are asking if their immune response was key - and if it could also be triggered by the vaccine
The patient, who was unnamed but was featured in a paper in the British Journal of Haematology, had not yet started chemotherapy for the disease, called Hodgkin lymphoma — a type of blood cancer that affects about 2,100 people a year in the UK.
So the sudden disappearance of the cancerous cells that had riddled his body was a complete mystery.
The possible efficacy of BTK inhibitors lessening the effects of COVID-19
Britain is launching a study to examine whether patients with immunosuppressed conditions have a less effective immune response to Covid-19 
Covid 19
