Here’s an example on how you an do this using Delta Time.
Every Tick you multiply ChangeRate with Delta Seconds. This means the ChangeRate is a per second type of value (in my example the meter will change with 10 per second).
After that you take the result and subtract from the Meter value. You may want to add functionality to reset the Meter and so on. Also you can simply set default values on Meter and ChangeRate, you don’t need the BeginPlay node but it makes it easier to screenshot.