I had a few months old SQL database backup on my PC. I opened it on Wordpad and searched for the link and found it there. Now I'm thinking, I can take a latest db backup, download it, open it on wordpad, edit the link and make it https, upload it and restore it. But this entire process will take TOO MUCH time (especially the downloading and uploading) as the db size is 1.5GB. Is there any way to find this link in the phpmyadmin like I did on wordpad and edit and save it?
If you found the link in a backup file, then you should be able to figure out what table and column it's in. If you tell us that, we should be able to tell you where you can change it in the admincp. Or at least it would be easier to find where to edit it in phpMyAdmin.
Be careful of what you edit directly in the database. If you edit a text field which is in serialized format you can make it invalid. If at all possible you should have a current backup before making changes.