HelpDesk REST API relies on SharePoint’s REST API, so you can use OData queries with such parameters: $select, $expand, $filter, $top and $skiptoken.
By default all queries will return the first 50 items, but you can return to a maximum of 100 items with the $top query option. Also you can page through returned items with the $skiptoken query option. Example usage (note single quotes in $skiptoken): _api/v4/tickets?$top=100&$skiptoken=’Paged=TRUE&p_ID=5’.