Reseting the trophy count from the admin panel, should not pose a problem for receiving trophy points in the future. Maybe that user is not getting any trophy points and that is why it is not doing anything.
It might be worth to run Update User Trophies cron. If that user has received trophies, rebuilding the trophy cache can solve the issue.
WHERE user_id = 123;
UPDATE xf_user AS u
SET u.trophy_points = (
FROM xf_user_trophy AS ut
LEFT JOIN xf_trophy AS t ON (t.trophy_id = ut.trophy_id)
WHERE ut.user_id = u.user_id
WHERE u.user_id = 123;
Replace 123 with the user id number.
The rest of the instructions are the same as that link I posted.