You have a couple options.
If you have access to the command line, you can attempt to manually create the symlink yourself. It's possible they disabled the PHP symlink() command, but the OS ln command may still be available to you. From the command line:
ln -s /path-to-project/storage/app/public /path-to-project/public/storage
If you don't have access to the command line, you can attempt to run the command from PHP using one of the program execution methods (exec(), shell_exec(), etc.). However, if they've disabled symlink(), they've probably disabled all of those, as well. To attempt this, create a temporary route, hit it once, then delete it:
Route::get('temp-create-link', function () {
exec("ln -s ".escapeshellarg(storage_path('app/public')).' '.escapeshellarg(public_path('storage')));
});
If you don't have a way to run the ln command, or if it has been disabled at the OS level, then you'll need to manually create your public/storage folder and update your filesystem config to point to it. Once you've created the public/storage folder, open your config/filesystems.php file and update the root key for your public disk to point to it:
'disks' => [
// ...
'public' => [
'driver' => 'local',
// old value: 'root' => storage_path('app/public'),
'root' => public_path('storage'),
'url' => env('APP_URL').'/storage',
'visibility' => 'public',
],
// ...
],