SQL Query for timeseries

I have 3 Tables

1. time series
2. timeseries2asset
3. asset

for asset, i am using this sql query

 SELECT
-- CAST(a.`tag` AS STRING) AS name,
-- CAST(a.`description` AS STRING) AS description,
-- CAST(a.`sourceDb` AS STRING) AS source,
CAST(a.`externalId` AS STRING) AS externalId,
-- MAP(
-- 'key', CAST(a.`key` AS STRING),
-- 'updatedDate', CAST(a.`updatedDate` AS STRING),
-- 'createdDate', CAST(a.`createdDate` AS STRING),
-- 'isCriticalLine', CAST(a.`isCriticalLine` AS STRING),
-- 'areaId', CAST(a.`areaId` AS STRING),
-- 'isActive', CAST(a.`isActive` AS STRING)
-- ) AS metadata,
-- CAST(NULL AS LONG) AS parentId,
CAST(a.`parentExternalId` AS STRING) AS parentExternalId
-- 7470047 AS dataSetId,
-- ARRAY(NULL) AS labels
FROM `CognitePOC`.`assets` a

for timeseries i am using this query

 select
   cast(`external_id` as STRING) as externalId,
   cast(`name` as STRING) as name,
   cast(`is_string` as BOOLEAN) as isString,
   cast(`unit` as STRING) as unit,
   cast(`is_step` as BOOLEAN) as isStep,
   cast(`description` as STRING) as description,
   7470047 as dataSetId
 from
   `Cognite`.`timeseries`


I have 3rd csv as timeseries2asset i want to update time series and i have to connect them to the asset how to do that

timeseries2asset columns - Key, externalId, sourceExternalId, targetExternalId