Hi Sanjay,
To achieve something like this, you may try creating a Block Element with a setup like this: https://share.getcloudapp.com/9ZumWP51
Also see: https://share.getcloudapp.com/04uEkr9A
As shown, I have a Button within a Container Block, and this Container has a custom CSS class make-bottom-fixed. Then, I added this CSS to make it fixed:
.make-bottom-fixed {
position: fixed;
bottom: 0;
left:0;
background-color:white;
width:100%;
}
Here is an article with regards to adding CSS: https://docs.generatepress.com/article/adding-css/#additional-css
Adding it through additional CSS should work.
Hope this clarifies. 🙂