Update Table Assistance Needed

Hello,
I am trying to update a table based on values that I have imported into a temporary table. Basically I have a list of lab codes (EMR_temp_labtest_configupdate) and each lab has a zseg code tied to it. The definitions for zseg code are in a separate table called (EMR_zseg_code_descriptions)

I need to update the lab_test_add_conf to add in each lab code that does not have any configuration information (not exists in lab_test_add_conf) based on the zsegcode.

For example a zsegcode (defined in the emr_zseg_code_descriptions table) is ZBL and the lab code 003277 fits into the zseg category according to the temp table. For each lab code that first into the ZBL category a row needs to be inserted for

Example of table data:

emr_temp_labtest_config

labtestcode, zsegcode
003277, ZBL

emr_zseg_code_descriptions
zsegcode, valuecode
ZBL, PATRAC
ZBL, HERITG

I want to look at the data in the temp table and determine which category it is in and then insert into the lab_test_add_conf table a row for each lab test each zseg table value code that exists.

My Final Goal:
lab_test_add_conf:

lab test code, valuecode
003277, PATRAC
003277, HERITG


I know I need to do an update statement but I am not sure how to set up the SET statement or if there is anythign that I need to take into consideration. Here is my code so far.....any thoughts?

select a.labtestcode
from EMR_temp_labtest_configupdate a
Where Not Exists
(Select *
From lab_test_add_conf b
where a.labtestcode = b.labtest_key)

update table lab_test_add_conf

select a.labtestcode,b.zsegcode,b.valuecode,b.valuedesc,b.valuetype,b.units,
b.tablename,b.fieldname
from EMR_temp_labtest_configupdate a
join emr_zseg_code_descriptions b on a.zsegcode = b.zsegcode