Hi Rafael Ortiz,
Thank you for using Syncfusion products.
Based on the provided information, your requirement of “Modifying the of picker based on the value of another picker” in Xamarin.Forms can be achieved using the UpdateEditor property of DataForm.
We have prepared sample based on your requirement, please find the sample by the following link.
In the sample, as per your requirement we have modify the city picker value and ItemsSource based on the value of Country picker.
We hope this helps. Please let us know, if need any further assistance.