Open studio pro 9.21. Search for project and open the development line you want to convert.
Note that when opend in newer version and committed to team server, roll back to previous isn't possible unless rollback full revisions. In short, only convert and commit if you want to continue with this version.
Hi Michael Deng,
You can create a branch line from your working main line ( 9.20.0) and then open the branch line with a higher version of studio pro ( in your case 9.21.0), while opening it will ask you to convert and click ok.
You can later delete your branch if needed.