Adding Custom Button or Text

Hello, I was wondering if there was a way to add a custom text button and/or the subtext “to add a custom tip, please manually enter an amount below” above the value box? Currently, the plugin allows for the admin to choose the rate of additional charge and allows for a user to enter a value into the value box. However, there isn’t an option to add additional text above the value box nor button. I’m new to coding & am unsure of where to exactly edit the plugin code so that it can reflect what’s desired.

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