I tried to clone the existing search and create a new search. Now my both the search services are active. How to make the old one as inactive? I cannot delete the old one without being sure of new one working as expected.
Search Topology has a specific meaning. It sounds like you're talking about a Search Service Application, instead.
What you can do is unbind the to-be-decomm'ed SSA Proxy from your Web Applications. Validate you can search/search works as expected with your Web Applications. Once validated, delete the old SSA.
Look into service application association. You can change the association from old search app to new one, then test when you are good you can just delete the old one.