In error reporting, how can we set an alert whenever a particular error occurrence is more than a threshold in a particular period?
For Example in the below screenshot, the occurrence of second error is more than 30 times in last 7 days. I want to setup an alert for all those error which are occurring more than say 10 times in last 1 day?

There's no way you can set multiple thresholds for one policy and generate different alerts.
You need to create another alerting policy that will count all the errors in the given timeframe (1 hour, day etc) and act on it accordingly.
Have a look at some examples utilising MQL language that's quite flexible and may give you some ideas.
What you need is a perfect example of a feature that you may request on Gogle's IssueTracker - explain in detail what you need, provide some exaples and wait for reply.