how to insert same data based in deffrent table based on checkbox ? mysql php

i want to insert data in multiple table

i have two tables> recharge due_user reacharge table has

ID - MOBno- AMount - Network

due_user has

ID - userID - MOBno - Amount - NETWORK

in my form i have checkbox which will ask userID only if i click checkbox.

now insertion of data procedure would be ..

if unchecked data > ID - mobno - Amount- Network will be inserted in Recharging table if checked data > ID- userID - mobile - amount - Network

will go both table Recharge and Due_user table
but user id will we goes into only due usertable