How to downgrade IntelliJ to older version

I have intelliJ 12 30day free software installed with entire project setup and running ; now I have a license received from my company and it is not allowing to register; then realised it is a license of intelliJ 11 version; please lemme know steps to downgrade to intelliJ 11. Like running a patch or what is the solution?

Download and install the old version from this page.

Another option is to use the JetBrains Toolbox App. It allows to install multiple IDE versions, perform rollbacks if needed, applies updates to the IDE and plug-ins, etc.

My operating System is Ubuntu 18.04 I downgraded my Idea community edition version 2020.3 to 2020.2 because it was causing so much lombok issues by using the following steps:
Step 1 : open ubuntu software search idea community click on channel version select version you wish to install and it will downgrade your version with all settings restored. if you dont want previous settings then just clean uninstall idea

simplest way for Mac users with TimeMachine:

1 open TimeMachine

2 select time before Idea upgrade

3 navigate to Applications

4 select IntelliJ Idea app

5 [Restore] -> [Replace]

I have successfuly restored Idea this way because of plugins compartibility.