Exploiting XXE via File Upload

Before moving further we must get familiar with XXE. So please check my previous blogs on it.
https://medium.com/@gupta.bless/exploitation-xml-external-entity-xxe-1f5f3e7bc5c4
We have learnt about XXE previously but there is one more thing we need to understand before going ahead, unrestricted file upload vulnerabilities. So you can read my previous blog for that one as well.