Laravel: Controller class Global variable returns null in class function

I'm a java developer; New to Laravel and PHP both. I learned how to define a global variable in Laravel controller class and used it as such. But it returns null in all other functions.

I have a class variable $person in my AddPersInfoController.php.

I initialize it first in a function because I need this ID to be saved with every record in different tables (handled by different functions in same controller) of the Database. But when I try to use it in any other function at the time of submitting form, it returns null.

Initialization function is called in get route as such:

Route in web.php

Route::get('/add_all/{persId?}',[AddPersInfoController::class,'add_all'])->name('add_all');

My AddPersInfoController.php controller

class AddPersInfoController extends Controller
{   
    private $person     ;
    
    public  function add_all( int $user_id){

        $pers   = $this->person = Pers_info::find($user_id);
                dd($pers); // This shows all values fetched from Database
                .
                .
        }

Here I initialize it and copy it into a local variable pers to pass it to the view using compact() method with a few other local variables.

In the view, I enter the data in other fields as required and then save them using a post route.

In web.php

Route::post('/add/prom_hist',[AddPersInfoController::class,'addPromHist'])->name('add_prom_hist');

AddPersInfoController.php controller

public function addPromHist(Request $request)
    {
        $this->validate ( $request, [
            ......
        ]);
        
        dd($this->person); // This returns null.

                $promHist = new Prom_history();
        
        $promHist-> pers_info_id     =       $this->person->id ; // I have to use it here
        $promHist-> date                =$request->date ;

It reutrns null in the above function.