Hi,
Our confluence was end of license and due to the recent hack problem we had to update it to latest stable. Meanwhile there was collation issues like in the screen shot.

ref:- https://confluence.atlassian.com/x/voTcDQ
So solution was Convert from MySQL MyISAM to InnoDB Storage Engine, I used the above doc and setup fresh installation of confluence with new database and new installation locations, eg:- /var/atlassian/application-data/confluence_2019/ and /opt/atlassian/confluence_2019 up on proceeding with database configuration it has asked for restoring a site option.
ref:- https://confluence.atlassian.com/conf59/restoring-a-site-792499608.html
We had backup of our old confluence install in /var/atlassian/application-data/confluence/backups/backup-2019_03_27.zip and it was moved to /var/atlassian/application-data/confluence_2019/restore/ and was able to restore good. I could see interface finished the restore good.
But after restore our Jira and confluence integration was lost and our existing confluence users unable to login, What I understand is jira and confluence versions miss match, we have latest confluence but Jira is end of license one. Password reset for existing uses are also not working as password reset is throwing exception. See the attached images.

Finally i have managed to setup "recovery_admin" account in confluence with password and manage to access updated confluence. I could see all our data here. I have tried to reset password of my login after login using recovery account meanwhile I am getting same error while trying to reset using password reset email.
Ref https://confluence.atlassian.com/doc/restore-passwords-to-recover-admin-user-rights-158390.html
How can I get my existing users work ? Is integration possible with existing jira version JIRA v7.1.7 and confluence confluence-6.15.2 ?