By default, the File Upload field can upload a single file only, but if you enable the multiple files feature, your form visitors can upload several files at the same time. To enable this feature, go to the Form Editor and add the File Upload field to your form.
Now select the File Upload field and go to the Edit Field panel, on the left. Next, check the box Allow multiple files, under Validation, and that’s it.
Your form users will have the Add Files button on the form that they may use to upload multiple files. All files will be displayed on the form, one below the other. The form visitors may use the X symbol on the right side of each file to delete it.