Gauge/Meter into stamina bar

Hey guys I want to change the gauge/meter into a stamina bar. Where it would regenerate slowly over time. Right now I don't see any options to have the gauge be full at the start of a match and have it regenerate slowly as the match progresses. The training mode has a refill option but I want a gradual refill and not a instant one.

If any one has any idea how to implement this please let me know!

Thanks guys!!!