Joining table columns works,auto_increment ID still blank

Hi I have been updating one table using another table like so:

SELECT msrp
FROM distlist
LEFT JOIN products
ON distlist.msrp=products.ProductMSRP

ive updated a bunch of columns like this and its perfect, the issue i have is that the ProductID which is an auto_increment column is blank. how can i "fill" this in to have the same amount of cells in other columns?

thanks for the help Andre