The closest answer is this one, and here's a line from it:
hg revert -r <oneRevBack> fileName
The last thing is to get <oneRevBack> other than using hash. I would dream of just typing <-1>.
The hg syntax for "one rev back" is tip^, where tip is the latest revision and ^ means "parent". If your working directory is not at tip, use .^, where the dot means "current revision".