Copying data from selected fields in previous record on a tabular form

I want to copy data from selected fields in a record on a tabular form
(called 'ProductUpdate') to the next record when those two records have
a common field - called 'BaseFund' . The selected fields I am
updating are called 'date' 'cash' 'shares' and 'gilts' (amongst
others).

After completing all the fields in the first record I would like all
the selected fields in the record below to be automatically updated if
I double click on the Basefund field of the second record.

I am sure this is possible but it is many years since I initially
programmed my database. At the moment I am using the Control ' keys in
each field to enter the duplicated value and this is rather slow and
long winded. Can anyone please help with the language to type in the
Double Click Event procedure section.

I hope this is clear enough. Many thanks.

Dave k