If you want add dynamic date or yesterday date in email body using ssrs tool SQL Server 2017, please fellow these steps:
Step 1>

Upload rdl file .
Step 2> Right click on file

Then click manage

Step 3> In Left menu click Subscription

Step 4> Click New Subscription

You will see this window

Then choose data-driven subscription

Then click edit dataset

Then you will get below window

From this select custom source you will get below window

after filling all type query like you want yesterday date then type below query:

Then click Validate Query AND APPLY
IN SUBJECT TAKE VALUE FROM DATABASE AND SEND MAIL