Update Aggregate Total

Update Aggregate Total

Hi,

Firstly apologies if this is something simple but I can't seem to get the workflow to work.

I have two forms.

Form A - Kits
Form B - Assets

Multiple Assets can be added to a single Kit. Joined with Lookup fields. 

Each Asset has a rental value (FormB) which by using an aggregate workflow in form A calculates the sum of all Assets and adds a value to a total field in form A. 

This all works as it should and gives the correct total.

The problem is that if I update the rental value in Form B the sum in Form A is not updated until I update the Kit record in Form A. I would like to make this happen on successful update of Form B. 

What would be the onSuccess workflow on Form B to update the total in Form A.

Any help would be greatly appreciated.

Thanks

Mike