Retrenchment Calculation - unit is going to be closed because of low production and non-profit making

Dear Experts, Can anyone guide with the calculation of Retrenchment!
Please note one of our existing manufacturing unit is going to be closed because of low production and non-profit making since lockdown started and management decided to not to continue with that unit. Most of the workers are permanent workers, few workers are working on third party payroll and few staffs also will b eligible for retrenchment.
Any suggestion/ guidance with the process and calculation will be a great help.

Dear Paul,
Elaborate answer can be given if you provide the the average no of employees on roll in the cadre of "workman" u/s 2(s) of the ID Act,1947 during the preceding 12 months period in the establishment on the date of the proposed retrenchment.