gistfile1.txt

public class AssignLeadsUsingAssignmentRules
{
    @InvocableMethod
    public static void LeadAssign(List<Id> LeadIds)
    {
        Database.DMLOptions dmo = new Database.DMLOptions();
        dmo.assignmentRuleHeader.useDefaultRule= true;   
        
        List<Lead> Leads = [select id from lead where lead.id in :LeadIds];
        for(Lead ld: Leads){
          Leads.setOptions(dmo);
        }
        if(Leads.size() > 0)
        {
          update Leads;
        }
    }
}