Virtual column that references a data from a related row

I have Valets ok

They have assignments (shifts)

They clock in, when they clock out I want them to enter their tips

the tips get added to a column in the assignment table

I want to be able to track the total amount of tips on the valet table

i created a virtual column called [tips] under valet but can’t get it to reference specifically ‘Related Assignments’ (not every assignment, only the ones they worked)

I can’t reference the virtual column to get the SUM of the tips,

Should I create a new table for ‘Assignment Data’ which would include: clock in clock out tips ect or can i reference the related data some how?