Set as Primary Name is used to resolve your wallet address to your ENS name.
Primary Name can only be set by the wallet that is listed as the ETH Address.
However if a name's Manager/Owner is connected, the button will also be visible and first update the ETH Address to theirs, then set of the primary name as a second onchain transaction.
1. Select Set as Primary Name
Go to Profile-tab of your name and click the Set as Primary Name button.
In this example the ETH address is a different to the Manager.
2. Review changes and update ETH address (if applicable)
If your ETH Address is missing, or not the same as the Manager, you will be prompted to update it.
Click the start-button to update the ETH address.
Then Open Wallet and confirm onchain.
Wait for the transaction to complete then click next.
3. Open Wallet and confirm onchain
Open Wallet and approve onchain transaction to "set the primary name for your address"
Wait for the transaction to complete, then click Done