The ideal place would be to do this in the on-commit event handler. You should add a microflow there to calculate the value of “Account”
In your case, you can call a microflow for opening the page for user input.
In that microflow, retrieve the object you want and return from the microflow as a data source.
Use Data view and place your input inside that data view based on attribute you want.
This is just like and edit/update information.