How Do I Increase Gravity Overtime If My Player Stays In The Air Longer?

It's hard to give any specifics without you providing any code, but the basic idea would be to have a value that gets set to the default gravity in each FixedUpdate you are grounded, and increase the value by a set amount each FixedUpdate while not grounded. Then, apply that value as the gravity for the player.

If you were using a Rigidbody2D, you could simply use the component's builtin gravity scale:

 public float defaultGravity = 1f;
 public float gravityIncreasePerSecond = 0.2f;
 
 private void FixedUpdate()
 {
   if (grounded)
   {
     rigibbody2D.gravityScale = defaultGravity;
   }
   else
   {
     rigibbody2D.gravityScale += gravityIncreasePerSecond * Time.deltaTime;
   }
 }