Need help creating a HELOC calculator - adjustable interest rates

[maddladdCHADD]

Howdy my name is Chadd I'm a mortgage loan officer.

I am looking to create a Home Equity Line of Credit calculator.
I need the ability to see the amortization / payment / payoff term given the rate adjusting throughout the term years.
I've seen amortization templates however they come with one rate that I can't change to illustrate how the payment and payoff duration would change as the rates change.

For example a 240 month, 20 year term
75000 Starting principle balance
*Suggesting that the rate for the first year is 11 - next 2 years at 6% - next 2 years at 3.5% - etc

Any assistance either in the form of a template or formula I can use to create this?

Thank y'all in advance!