You can't.

No.

An autonumber has ONE PURPOSE ONLY: to provide a unique, unrelated to anything
else, not dependent on anything else, meaningless identifier. If you want to
control the value of a field, you *cannot* use an autonumber for that field.

I still strongly suspect that your table design is at the root of your
troubles, but if you really do need a one to one relationship between two
tables, using the same value as the primary key, then the second table's
primary key must be a Long Integer number, *NOT* an Autonumber. You can have
it fill in automatically by using a Subform, using the autonumber field as the
Master Link Field and the related long integer field as the Child Link Field;
or - if you insist on making your job and your users' jobs harder - put VBA
code in the form-open command and the form's Open event to pass the autonumber
value via the form's OpenArgs property, and set the default value of the child
table's primary key in the popup form's open event.

So... STOP. Your first step should be to review the normalization of your
table structure. If you keep fighting with forms, adding new controls, adding
new tabs, adding new forms to overcome a flawed table design, you're on the
wrong track! "If you find yourself in a deep hole, the first thing is to stop
digging".

We're not attacking you here, Janet. We're trying to help. We've all been
where you are now, and have gotten help from others - and found that properly
normalizing data really DOES make a big improvement, as soon as the (rather
steep and rocky) learning curve is climbed.