Gdevelop 5. mechanics of oxygen

Good Morning. How do I make a mechanic who needs to collect an object called oxygen? if the player does not collect, a bar or countdown will constantly run out, causing the player to die when it reaches 0

The oxygen meter have to going down in every frame, hold the value in a variable. If the character touches one of the oxygen objects then remove that oxygen object from the scene and add some ammount to the oxygen variable value.