Change Subdomain of tiki installation
One thing i always liked about Tiki compared to some other popular CMS's is that Tiki doesn't really care where it is, move to a different sub-domain, or put it in a nested directory and (usually) it doesn't make any difference.
So you should be fine, but of course make a backup first (and often). Just about all you need to do is make a backup of the database, and any theme customisations. To backup the database you can use any of the database management tools (phpmyadmin or adminer for instance) or you can use the console.php command, e.g.
php console.php database:backup /home/backups/
For busy, precious, sites i'll also often set up an hourly cron job with a command like this to backup the data every hour, just in case:
cd /wherever/your/tiki/is; php7.4 console.php database:backup /home/backups/hourly/ H00\\\h > /dev/null 2>&1
so you can roll back up to 23 hours later (then also have a daily and weekly/monthly backup too)
HTH