The new installer at https://gitlab.com/wikisuite/wikisuite-packages will offer auto-updates, but if you installed before, you need to update manually:
Virtualmin Tiki Manager
cd /usr/share/webmin/virtualmin-tikimanager git pull
If you get an error because your source code has been modified ("Your local changes to the following files would be overwritten by merge"), here is how to restore to the unmodified state:
git checkout -- .
If you get an error, about permission denied (public key) on GitLab. please see: https://stackoverflow.com/a/58082435
Tiki Manager
cd /opt/tiki-manager/app php tiki-manager manager:update