How to add a CDS service bound action parameter with default value

Hi expert,

I wound want to create a service action. there are 3 parameters, and i want the first parameter is fixed value from one entity field.

as below example, i want inputCheckpointId is fixed value from entity

entity VDiffWithRule

as select from testauto.VDiffWithRule

order by seq

actions {

action editDiff(inputCheckpointId:UUID, variable : String(50), skipCheck : Boolean) returns VDiffWithRule;

};

but i don't know how to implement it, could you kindly guide me?