I want to activate 2019 version as well as 2021 version, but I can't.

On my old computer, both the 2019 and 2021 versions were available.

Now I got a new computer and I have deactivated the 2021 one on my old computer and activated on my new one, but I cannot do so regarding the 2019 version.

Oana tried to help me on online chat but it didn't work out.

Please help me to use 2019 because I need to use the older version for compatibility.

Thank you.