V14 data allocation from a child table to an employee Doctype

Hello Everyone,

I mainly work with 3 Doctypes, “Employee” “Project” and “Employee affect” and since i can’t link the Employees as a table, i created the Employee affect as a child table Doctype to Link them in the Project Doctype as a table, the field that links in the “Employee affect” Doctype is “employe_aff”, the name of the table created which is linked with the child table in the “Project” Doctype is “employeestab” and the name of the project is the “project_name”
So i want everytime that i create a Project and add records on Employees and save, i want it to automatically allocate the “project_name” for every employee that ive added on the table for the field existing in the Employee “projet_affectee”.

Can someone help please? Thank you all for taking your time