Change the query to:
$query = "
select
user_first_name
, user_surname
, user_email
, user_mobile
from
user_info
where
user_id
like
'%" . $trimmed ."%'
or
user_first_name
like
'%" . $trimmed ."%'
or
user_surname
like
'%" . $trimmed ."%'
order by
user_id";
See what gets returned