First it would be a good idea to contact a Fortinet Partner with knowhow with that products for the next time, especially if it's for your main business . There are a reason, why network specialist are existing. ;)
First important thing to know is, that the cluster are in sync only when both Firewalls has the same firmware version. If you have a firmware mismatch the cluster come never in sync.
In your case, and with the minimal information about your infrastructur, I suggest the following steps:
- Create a backup from the firewall with the correct configuration (always, create a backup before you upgrade)
- Shutdown the firewall with the Version 7.0.7
- Upgrade the firewall with the Version 7.0.5 to 7.0.7 -> Wait until upgrade is success
- Start the firewall from the first step again
- Check if both firewalls see each other (System-HA in the Menu)
- Wait 1-2 hours for sync between both members
There is no way without downtime, in my point of view.
If the cluster still "out-of-sync" after a couple of hours, you can start again with your troubleshooting.
- Have you found a solution? Then give your helper a "Like" and mark the solution.