Hi Parinaz,
For your question, I don't really understand ‘select one of them as the main address field’.
Do you want to just one address field in the form?
If so, you can lock or hide other address fields that you don’t need.
Go Settings > Customization > Customize the System > Entities > Contact > Form.
Double click the field and open ‘field Properties’ dialog.

If my understanding is wrong, please provide a more detailed description or screenshot.
Regards,
Leah Ju
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