list - C++ - fatal error LNK1120: 3 unresolved externals, can't find solution

So, I'm having problems with my code. I'm simply trying to run an example code to see how it works (I'm a newbie at C++) and this error is appearing everytime I call the List class.

Here's the code:

//main.cpp
#include 
#include "List.h"
using namespace std;


int main() {
    List list;
    // 5 types created using a 'for' loop 
    // and calling the ‘add’ function

    for (int i = 101; i <= 105; i++)
    {
        list.add(char(i));
    }

    list.display();
    // should output a, b, c, d, e 
    // in this example.
    cout << endl;
    return 0;
}

And here's the List class

//List.h
#pragma once
#include "Link.h"

template  class List
{
private:
    Link* head;
public:
    List();

    int add(F theData);
    void display();
};

and I'll also put List.cpp to help:

//List.cpp
#include "List.h"


template List::List()
{
    // 'head' points to 0 initially and when the list is empty.  
    // Otherwise 'head' points to most recently 
    // added object head
    head = 0;
}
template void List::display()
{
    Link* temp;// 'temp' used to iterate through the list

                  // 'head' points to last object added
                  // Iterate back through list until last pointer (which is 0)
    for (temp = head; temp != 0; temp = temp->Next)
    {
        cout << "Value of type is " << temp->X << endl;
    }
}

template int List::add(F theData)
{

    // pointer 'temp' used to instantiate objects to add to list 
    Link* temp;

    // memory allocated and the object is given a value
    temp = new Link(theData);
    if (temp == 0) // check new succeeded
    {
        return 0;  // shows error in memory allocation
    }
    // the pointer in the object is set to whatever 'head' is pointing to

    temp->Next = head;
    // 'head' is re-directed to point to the last created object
    head = temp;
    return 1;
}

When I run, It gives me these errors:

errors

PS. I'm using VS2017 btw.

Thank you