Go to your PSA, add a company.
Go to Strategy Overview:
Settings --> Integrations --> PSA integration --> "Companies" tab
Click "Import Companies button:
In "Import Companies" popup:
1 - Click "Load companies". Use filters to find a needed company.
To apply filters you need to press "Load Companies" button every time you change filters.
2 - Mark a Company.
3 - Click "Import".
Find a new companies in the right part of the screen - in "You PSA Companies" list, it will be marked as "Unmapped"
1 - Click "Create new" button near the company
2 - Click "Save mapping"
If you have Assets and Contacts integration enabled, the system will ask if you want to sync it too. You can confirm or cancel (and setup it manually or later).
Done! Don't forget to add a group in a company card to setup assess for users to a new company.