Rabbi Gourarie has advised the following:
The optimum way of doing Mechiras Chometz with Rabbi Gourarie is in person.
However, in the current situation with the Corona virus, do not go to Bina or to Rabbi Gourarie's home to give him your form.
It is quite acceptable to complete and sign the form, then scan or photograph it and email it to the office (details are on the form).
If you don't have a printer, use the Word version of the form to fill in your details, and type your name in the space for your signature. Under the circumstances, that will be treated as a signature.