A valuation is carried out by authorised firms and their representatives (usually banks and their associated valuation experts) after taking into consideration recent property transaction prices, as well as other market factors.
You can also ask a real estate agent or mortgage broker for an indicative value. Apart from that, you could engage the services of a registered valuer for an official valuation report for a fee. For example, you can refer to http://my-property.com.my/
Here's a comprehensive guide on how property valuation works: https://www.propertyguru.com.my/property-guides/how-property-valuation-works-14584
Hope this helps!