Now after two days I am unable to send and receive emails from outside mail providers such as gmail.

Whereas internally mails are working.

Now I am getting message to log on DNS server, make DKIM entry...

We are small startup and do not know these terminology. And I cant find any tab to configure DNS setting in zoho admin panel.

We we had so technical knowledge, had we created free account with zoho?

Please help me with fixing this issue.