Asking for my old job back?

Hi r/jobs/, basically I just got let go from my current job today. I gave my two weeks notice today and then I had to go home cause I had a fever and then I told my boss I couldn't come tomorrow cause I was diagnosed with strep. And then an hour ago I was told to not come in Monday.

Luckily for me, in my previous job before the one I was let go from today I left on good terms with my old supervisor and I still have his number. What would be a good way to ask for my old job back?

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