If both of your nodes has failed/restarted first thing to do is to check if data on both servers is consistent.

Now you can start restoring configuration. In order to do that we have two possible solutions:

First solution:

go to the Primary node:

SETUP-> network-> Failover-> Function: Failover Manager click Stop and wait until the process will be finished. After that click Start and wait a second so the nodes can configure themselves again

Second solution:

go to Secondary node:

SETUP-> network-> Failover-> Function: Failover Manager  and click Sync volumes. After this process is finished click Failback.
If there are no other problems your failover should be running now.