If input.is action just pressed(jump):
Hold on to jump input for 1 second.
If is on floor and jump input is true
Velovity y = 2
So basicly if the player presses jump when he is just above the floor the script hold on to the info of jump pressed for 1 second and if in that 1 second timeframe he touches the floor it jump.
You have in your script a boolean variable called something like wants_to_jump
Whenever the player presses the jump button, you set wants_to_jump to True, and start a 1 second timer.
When that timer runs out, you set wants_to_jump to False
Every frame, if the player is touching the floor, you check if wants_to_jump is True, and if it is, you make the player jump, and also set wants_to_jump to False.