how to identify and set User model foreign keys in User details database on submitting my User Registration form

As I mentioned above I want to automatically identify the User's id from the User model and set it in my User details model as foreign key on Submitting Registration form curenty I am making changes manully to testing purpose which is not a practice for standalone website

models.py

    class Student_Details(models.Model):
        u_id=models.ForeignKey(User,null=True,on_delete=models.SET_NULL)
        field=models.CharField(max_length=400,null=True)
    
    class Institute_Details(models.Model):
        I_id=models.ForeignKey(User,null=True,on_delete=models.SET_NULL)
        name=models.CharField(max_length=400,null=True)
        zipcode=models.CharField(max_length=6,null=True)
        def __str__(self):return str(self.name)
    
    class Staff_Details(models.Model):
        s_id=models.ForeignKey(User,null=True,on_delete=models.SET_NULL)
        Institute_from=models.ForeignKey(Institute_Details,null=True,on_delete=models.SET_NULL)
        def __str__(self):return str(self.s_id)

form.py

class CreateUserForm(UserCreationForm):
    class Meta:
        model = User
        fields = ['id','username','first_name','last_name','email', 'password1', 'password2']

class Institute_form(ModelForm):
    class Meta:
        model = Institute_Details
        fields=['name','zipcode']

viewspy

@unauthenticated_user
def registerPage(request):
    form = CreateUserForm()
    form2 = Institute_form(request.POST)
    if request.method == 'POST':
        form = CreateUserForm(request.POST)
        form2 = Institute_form(request.POST)
        if form.is_valid():
            if request.POST.get('user_type') == 'User':
                user1 = form.save()
                group1 = Group.objects.get(name='Student')
                user1.groups.add(group1)
            elif request.POST.get('user_type') == 'Institute':
                user2 = form.save()
                form2.save()
                group2 = Group.objects.get(name='Institute')
                user2.groups.add(group2)
            return redirect('default')

    context = {'form': form,'Iform':form2}
    return render(request, "htmls/signup.html", context)



def logoutUser(request):
    logout(request)
    return redirect('default')