Hi @Gaurav-G_Chahar and welcome to the community!
In TMP there is no Epic Link field. Instead there are a couple of ways to link existing issues to Epics.
From an issue, navigate to the breadcrumbs and click "Add Epic". Then choose you Epic you want to connect it with.
From the backlog, open the epic panel. Click on an epic and then click view details. Click create subissues and then "Choose an existing issue":