Help with this project

Good morning, could you give me some help with this programming.
I am working on a project for a body and paint shop and I got stuck on this part.
I have a field called Position, it is a consecutive, this field is within a table called Budget Positions, from the budget table it makes a Relationship to position

 I would like to be able to ensure that in the relationship of positions within Budget the consecutive one when I create another budget the position field starts from zero, is it possible Thank you