To undo a git reset, you can use the command
git reset 'HEAD@1'
This will make the Git point to a version before the reset happened.
HEAD@1 means version before reset and HEAD@0 is the last git reset command itself.
This is possible since Git tracks all the activities within a branch including the git reset.
If you want a more detailed look into the activities in a Git branch, you can use the
git reflog
command. This will show all the activities including reset.