Build up Running Motion Using Tapping Method

Hi! I want to add a feature where a player has to tap a certain button repeatedly to run faster. Not just taping once by binding left shift key to run. But tapping the left-shift key repeatedly which will eventually make the character run faster than the default movement speed and able to hold the buildup speed by holding down the left-shift key button.

Btw I’m a beginner, would be appreciated if one could provide a step by step guide with or without screenshots.