How to round to the next Sunday - Rounding Rule for Derived Factors

I have created a new Length of Service Derived Factor with the following values:

Unit of Measure: Weeks
Period Start Date Rule: Seniority Date

I have used this in an absence plan matrix to create entitlement rules and it is working well. However, I would like for this not just to look at the seniority date, but to round to the next Sunday.

For example, if somebody's Seniority Date is '31/05/2024', it would instead use the date '02/06/2024' as this would be the next Sunday.

I have seen that the Rounding Rule can be set to 'Formula' - I assume this is the way to do this?