You can take the platform admin course on partner academy - It covers the topic needed for a platform admin quite well .

https://partner-academy.databricks.com/learn/courses/1230/databricks-platform-administration-fundame...

you might also want to look for cloud specific platform admin course on partner academy . 

Next would be to master data exfiltration architecture on databricks as explained on this link 
https://www.databricks.com/blog/data-exfiltration-protection-with-azure-databricks 

If you can use terraform to deploy a data exfiltration architecture on databricks that should give you a fairly good confidence as a platform admin on databricks .there is always more stuff to learn and master but this should be a sufficiently good start .