Welcome to the Bunnings Workshop community. Thank you so much for joining us and sharing your question about how do you repair the paint finish on a water-damaged external wall.
Thank you for posting a picture of the damaged area. The paint finish has been damaged due to over-exposure to water. The hairline cracks at the side of the damaged area will also need to be fixed. I suggest using a Trojan 6 In1 Multi Paint Scraper to remove all the damaged paint up to the hairline cracks.
When all of the paint has been removed from the damaged area. Observe if the cement is damp, if the dampness does not dissipate, water has settled inside. It will not be suitable for painting until the cement is dry. I suggest bringing a paint sample at least the size of a 1 dollar coin to your local store to get a paint colour match. Please make sure to tell the paint specialist that you are using the paint for a rendered exterior wall. Show the picture of the damaged wall to the paint specialist.