You can install CodeMix to Eclipse 2020-06 and prior versions without any additional steps. Once installed, go to Help > CodeMix > Update license and click ‘Login’ to enter your credentials.
Please note that CodeMix has already reached its end of life and no new releases or fixes will be made to it. MyEclipse is the alternative. See here for more details : https://www.genuitec.com/products/codemix/end-of-life-notice/
You can try MyEclipse for free for 30 days and if it fits your requirement, then we can convert your existing CodeMix license to work with MyEclipse.
Hope this helps. Do let us know if you have any further questions.