Customize form field

Hello, i’m trying to customize one of the form fields but can’t find out how to do what we want.
It has a field where people can choose the donation frequency period (daily, weekly, monthly, etc.), and below this dropdown field option it has selected by default the amount of donations.
Is there any way to make this field customizable and give the option for the user to choose how many times he wants this donation to occur?
Hope you can help me with this issue.

Thanks,

Matias

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