Is this what you are talking about?

Synchronize Subforms

Thanks Scott! Sorry for the delay,

I watched it and basically it's the same idea but my only problem is that it's connected in a form that already has data as well and for some reason the two subforms don't connect as nicely.

As long as the relationships are correct having data already shouldn't be an issue.
Can you be more specific as to "don't connect as nicely"?  What problems are you having?

Probably need to post some screenshots.

In the first image it's a form to keep track of suppliers and the products they sell.

There are two subforms, the left one is a product list form that lists all the items that the specific supplier sells, and the one on the right is a price update form that you can track changes in price per item.

What I want is that when I click oil in the Product List form the Price Update form will filter and show me only the price history for oil

Set the Record Source of the second subform to an SQL statement and add a where condition.
Then in the On Current Event of the first subform requery the second.
See my example below which shows how to accomplish what you want.

Hi Kevin,

I tried it but it still doesn't work, I don't know why since I did everything you wrote.

Gives me an error 2452 each time I try to open the supplier form

Which form's OnCurrent event did you put the code in?
Should be in the ProductSubF (or whatever you named your subform).

The one on the right, The PriceUpdateF

I changed it to the SubForm on the left and it filters it but when I click on the next item it doesn't change with it