Three questions, in order
<b>Who can enforce it?</b> Not everyone who would like to. The benefit has to have passed to the person complaining, and on old covenants it frequently has not. This is the first thing to establish and it ends a good proportion of threatened disputes.
<b>What do they want?</b> A neighbour objecting to an extension that blocks their light wants the extension changed. A company that bought the benefit of a covenant wants to be paid for releasing it. These are different disputes with different answers.
<b>What would a court give them?</b> Damages are the common outcome. An injunction — an order to stop or to undo — is available and is discretionary, and the more established and the more expensive to undo the breach is, the less likely it becomes.