convert a level 1 M file s-function to a level 2 M file st-function

how can I convert a level 1 M file s-function given below into a level 2 M file st-function?

function [sys,x0,str,ts] = potential_field(t,x,u,flag)

switch flag,

   case 0,
    [sys,x0,str,ts]=mdlInitializeSizes;

  case 1,
    sys=mdlDerivatives(t,x,u);

    case 3,
    sys=mdlOutputs(t,x,u);

   case { 2, 4, 9 },
    sys = [];

  otherwise
    DAStudio.error('Simulink:blocks:unhandledFlag', num2str(flag));

end

function [sys,x0,str,ts]=mdlInitializeSizes(~,~,~,~)

sizes = simsizes;
sizes.NumContStates  = 0;
sizes.NumDiscStates  = 0;
sizes.NumOutputs     = 5;
sizes.NumInputs      = 6;
sizes.DirFeedthrough = 0;
sizes.NumSampleTimes = 1;

sys = simsizes(sizes);
x0  = [];
str = [];
ts  = [0 0];



function sys=mdlOutputs(~,~,u,~,~,~,~)

%%% Paramètres de contrôle :

a0=0;
av=100;
c=0;           
b1=0;
b2=0;

                 
yub=u(4).*sin(u(4))+10;  %upper boundary
ylb=u(4).*sin(u(4))-10;  %lower boundary
y=.5*(yub+ylb);    %center line
  Urep_1=zeros(1,1);Urep_2=zeros(1,1);
  if (ylb<=u(5))&&(yub>=u(5))
      
      Urep_1=b1/(u(5)-yub)^2;
      Urep_2=b2/(u(5)-ylb)^2;
  end
  
  
  
J=@(X)(a0*(X(1)-u(1))^2 + av*(u(1)*tan(X(2))-u(6))^2 + Urep_1 + Urep_2 + c*(X(2)-u(3))^2);

X0=[1,15];          %Initial point for X
A = [];
b = [];
Aeq=[];            %Matrix for linear equality constraints	 
beq=[];            %Vector for linear equality constraints	 
lb=[0,-pi/2];	   %Vector of lower bounds	 
ub=[90,pi/2];      %Vector of upper bounds

Q=fmincon(J,X0,A,b,Aeq,beq,lb,ub); %% les valeurs réelles retournées sont la vitesse désirée et l'angle de lacet désiré
  
sys(1)= Q(1);
sys(2)= Q(2);
sys(3)= yub;
sys(4)= ylb;
sys(5)= y;