1. To bring the connection back online, you will need to go to Connections > Actions, then click on Edit connection.
2. For NetSuite connections, if they are set to Basic authentication, for security, it is recommended that you update to token-based authentication.
Note: If the above still does not work, you may use the next option which is Token Based Auth (Manual), to set this up, you will need to refer to the below documentation on the steps:
If in cases you will receive further error i.e. see screen shot below:
You will need to make sure the below highlighted feature is ticked: