how to assign users from contact listpage to selected records for listpage i will expalin my story clearly below

i want to select records from the list page then click multi Assign button then open page the have list of contact (user) here select number of users then assign those record to respected user. example select 4 records then click button then open page select 4 users from list of contacts name then assign accordingly.
here for selected records can get by collection parameter Nested param as Id so one by one it will take so i used subprocess for that guide me for that too.