Search for the company. If you find the company in the search results then there's obviously no need to add a new company which would create duplicates and confusion.
If it's just the company you need to add then click the "Add New Company" button at the bottom of the search results.
There's also a button to add a company and contact at the same time. This is pretty normal usage.
Select country and continue
Enter Postal Code
Select matching company / address
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