Valid_IF selection list and related column

[AGairAdmin]

user filling out a form

i have 2 tables and 2 columns

Table 1 = Company table  / Company name , Company Key
Table 2 = User table / Company name, Company Key

adding a record to table 2 "user table" 
"Company name" column = Valid_IF , references column "company name" on table "Company Table", that has the list to choose from 

That works 
when the company name is selected it needs to populate "company key" from the company table off the row with company name and insert it into the user table 


So,     
if im in the user table and select from list or dropdown on another table and select a company name we need it to populate the company key too from the reference table