Shimano's tech doc site doesn't even bring up a MF-HG20. However it does bring up a MF-HG22. It shows the removal tool being a Shimano TL-FW30. Whether the park tool
SurferRosa pointed you to is the same in every respect I do not know.
https://www.universalcycles.com/shop...s.php?id=17706
https://si.shimano.com/en/pdfs/ev/MF...20(Y)-1948.pdf
https://si.shimano.com/en/manual/sea...ut_model=mf-hg
Nor do I know if this is the tool you need.