How to restore a database to a point in time using a script in Microsoft SQL Server
You need at least two backups for this. One full backup and one transaction log backup. So first you use a command like your above command (but you can remove UNLOAD option, it is a dummy option when you restore from disk). And then you have something like:

RESTORE LOG MyDatabase 
FROM DISK = N'C:\Documents\BackUps\MyDatabase.trn' 
WITH 
 FILE = 1
,STATS = 5
,STOPAT = '20190308 11:31:50.237'


That log backup had to been produced after the point in time to which you want to restore. And since you need a log backup, you need to have the database in FULL (or BULK_LOGGED) recovery mode, not SIMPLE.