how to set the link in wordpress such that on clicking it doesn’t open another page but go to the bottom of same page

You should use anchors to do this.

From W3C:

When the name or id attributes of the A element are set, the element
defines an anchor that may be the destination of other links.

Authors may set the name and href attributes simultaneously in the
same A instance.

and…

The id attribute may be used to create an anchor at the start tag of any element (including the A element).

The id and name attributes share the same name space. This means that they cannot both define an anchor with the same name in the same document. It is permissible to use both attributes to specify an element’s unique identifier for the following elements: A, APPLET, FORM, FRAME, IFRAME, IMG, and MAP. When both attributes are used on a single element, their values must be identical.

So you need to place an anchor somewhere in your page and then set your link to point to that anchor (using # character).

For example:

Add this to your menu:

<a href="#anchor-one">Go to anchor one</a>

And this somewhere on your page:

<a name="anchor-one">This is the location of anchor one.</a>

You can also use id attribute as anchor. So this will work too:

<a href="#section2">Go to Section Two</a>
...
<H2 id="section2">Section Two</H2>