Is there anyway to force someone to complete a PayPal payment?

I am not sure if I understand your query correctly. Do you mean to say if you want to complete the payment from the incomplete payments? If so, unfortunately, it is not possible to complete the payment from incomplete payments. If you have enabled the Authorization only in the payment field to capture the payment later, you may charge the user later from the PayPal dashboard. However, this option doesn't charge the user immediately and it is required to charge the customers manually for all the submissions received while the option is enabled.

Hope this information helps! Let us know if you are referring something different. We will be happy to assist you further.