As you have purchased the template, you can refer to its original workflows, if you want to change any parameters there. Just, please, keep in mind, that it’s always better to make changes by testing out every step, in order to avoid conflicts within the setup.
As I understood from your message, you would like to change the parameters for new plans. I’ve made a short video for you, which shows where and how you can do that, using an example with the percentage value:
Regarding your second question - unfortunately, so far Zeroqode is not providing small customization works. Sorry for such inconvenience. From our side we are always happy to guide you through the process of the setup and troubleshooting (in case you will have any on the way), however, a step-by-step guide is not provided by our support team. That is a part of the Customization service.
What we can offer you is to hire someone for such kind of work (change few elements within the existing app), I would recommend checking the Freelance section at the Bubble forum: Jobs / Freelance - Bubble Forum or check on UpWork or Fiverr for Bubble freelancer development offers.
Let us know if you have any other questions.