This is only to change the amount that you contribute to the HSA. Once you submit, it can take up to two payrolls to update. It is your responsibility to make sure you are not exceeding the annual IRS limit if you increase your contribution amount. If you no longer want to contribute, then list $0. You will still be enrolled and continue to receive the employer contribution.
The HSA contribution limits for 2025 are $4,300 for self-only coverage and $8,550 for family coverage. Those 55 and older can contribute an additional $1,000 as a catch-up contribution.