When signing up with Covve you will be asked to choose the address book which you want Covve to be synchronized with.
If you select "Outlook" you will be asked for your credentials and to test the connection. In some cases Covve will not be able to connect to you Exchange server.
There are many possible reasons for this including:
a) The Exchange server is within a VPN and not accessible to the "outside world".
b) The server may provide access to the "outside world" (for example, through Outlook Web Access) but the specific services required by Covve may be disabled
c) The Exchange server version may not be supported by Covve (Covve support Exchnage 2010 and later)
If this is the case it is unlikely you will be able to synchronize Covve directly with Exchange. However, there are two alternatives:
a) If you have an iPhone which has access to your Exchange contacts then you can download the Covve mobile app and synchronize your iPhone (and, indirectly, your Outlook) with Covve.
b) You can also export your contacts from Outlook and import them into a gMail account which you then synchronize with Covve. You can find instructions on how to export from Outlook here and instructions on how to import from gMail here.