With the context you provided in mind, I think you mean you wanna control the speed of the character with mouse wheel. If that’s your objective, you can check out this post of mine 
If you want to have an automatic movement feature for the player character, you can create a timeline, put the Add Movement Input node after it’s Update pin and call it with a custom event by connecting it to the Play from Start pin. You can also set the speed to your liking before triggering the timeline, right after the custom event. And to reset the speed once the auto movement is completed, you can simply set the max walk speed (that you drag out from the movement component) to your desired value.
You can subtract the actor’s location from the target location, normalize the result with the Normalize node, and plug it into the World Direction pin of the Add Movement Input node.
Hope this helps! 