Hi @JyotiSharmaV,
You have to write custom code for displaying popup on the page.
Use form based composer to create a HTML offer which contains the HTML, CSS code for the pop up and the JS which displays the popup on page.
Additionally, You can refer to this link to add a pop up in Adobe Target in VEC.
https://experienceleague.adobe.com/en/docs/target/using/experiences/vec/modifications/experience-tem...
Hope this helps, Thanks!