This is a very deep topic so I can't really do it justice here, but as a starting point, grab the query from the report, run it on SSMS with the "show actual plan" option and you will see in the execution plan if it is doing index seeks in there.

At least it will tell you which part of the query is most expensive, but reading query plans in depth is not straight forward. Grant Fritchey (aka scaryDBA - works for Redgate who run SQL Server Central) has an excellent book on the topic.

You can also tune the query in SSMS but trying changes and verifying success (they run quicker and the execution plan confirms more efficiently).