I'm here to help you, @Vivianalv.
You'll have to enter the specific percentage or the exact amount and edit it every-time you run payroll. The system only detects a specific percentage or amount to set up the contribution. This way, you'll have your contribution portion in the right set.up.
You can always visit our Employees and payroll taxes page to learn some tips in tricks on managing your payroll in QuickBooks Online.
Also, in case you want to learn some "How do I" steps in QuickBooks Online, you can visit our Help articles page for reference.
If you have other questions or concerns, please don't hesitate to reach out to us. I'll be around to help.
