MoveTo:

:MoveTo, is a primary function of the Humanoid, it's purpose is to move the player.

local Player_Name = "Hillary"

game.Workspace[Player_Name].Humanoid:MoveTo(workspace.Part)

Parameters;

1st parameter; Position, this concludes where we want to move the player to, so in the code above me, we moved the player to the part.

Code;

This would move the player infinitely between the two points you mentioned;

local NPCName = "Max" -- the name of your npc
local Point_A_Name = "PointA" -- the name of the first place you want to move him to
local Point_B_Name = "PointB"

function Move(place)
    game.Workspace[NPCName].Humanoid:MoveTo(place)
    game.Workspace[NPCName].Humanoid.MoveToFinished:Wait()
end

while wait() do
    Move(game.Workspace[Point_B_Name].Position)
    Move(game.Workspace[Point_A_Name].Position)
end

Aha! There you go.

:MoveToFinished, waits until the player has moved to the specific point.

Improving your code, with pathfinding.

Let's say the path between the two points are very hard to get to, well in this case the NPC has no brain so it would walk straight into the wall if there was a hard path.

So we use PathFinding!;

local NPCName = "Max"
local Point_A_Name = "PointA"
local Point_B_Name = "PointB"

local PathFindingService = game:GetService("PathfindingService")

workspace[NPCName].HumanoidRootPart:SetNetworkOwner(nil)


function PathFind(place)
    local Path = PathFindingService:CreatePath()
    Path:ComputeAsync(workspace[NPCName].Torso.Position, place)
    local WayPoints = Path:GetWaypoints()

    for i, waypoint in pairs(WayPoints) do
        if waypoint.Action == Enum.PathWaypointAction.Jump then
            workspace[NPCName].Humanoid:ChangeState(Enum.HumanoidStateType.Jumping)
        end

        workspace[NPCName].Humanoid:MoveTo(waypoint.Position)
        workspace[NPCName].Humanoid.MoveToFinished:Wait()   
    end
end

while wait() do
    PathFind(game.Workspace[Point_B_Name].Position)
    PathFind(game.Workspace[Point_A_Name].Position)
end

maxpax2009 Here; Keep Scripting!

you can use a mixture of a For loop and Pathfinding Service