Autofill form and subform from login form

[patheo]

Dear All,

I am working on a POS database and have a form to register the sales. This form contains a subform that is linked to a table VTE. This table should register all the sales done by each user.

What I want is the following:

1- The field CAISSIER(E) to autofill the user_id of the user. (Done)
2- Fill the sales by inserting the CBARRE field and return to zero the subform by a click on a validation button.

Can you please help me on the point #2 ?

Find attached the database.

Thank you in advanced,

Pathéo,