[DManA]

Lots of writers have taken a crack at that question over the years.

The Connecticut Yankee did pretty well (for a while).

In another short story I read the poor modern man transported back discovered he didn’t have the tools to make the tools he needed to make modern technology.

[Reily]

A great SciFi read based on the Connecticut Yankee theme is
“Least Darkness Fall”, a modern man (I think it was written in the 1930s, I seem to remember a Mussolini reference!) transport to Ostrogothic Italy. The hero survives and pieces back together the Western Empire.