Promotion - Extra Month To Membership

I want to run a promotion where we can reward members with a complimentary one month (or more/repeated bonuses) extension to their paid membership.

A simple way to do this would be to go to their subscription and manually extend it, but there is no log/record of the reason and it is a bit long winded for my colleagues.

I have been trying to work out something on the Promotions area, but can't seem to utilise this.

Any suggestions on how an admin can apply a promotional membership extension?

If the plan is already month by month you could create a promotion to give them a free renewal, but aside from that there isn't really any features in place to give people time like that. You can also give them a free renewal within CB > User Management by editing them and checking the renew checkbox under the Subscriptions tab.

They are annual memberships I want to extend by one month....

There's no functionality for that. You'd have to directly modify their subscription and move their expiration date, which will not work correctly if you're using auto recurring payments.