Steps:
1. Sign in to your Twitter account and locate suspected spam account.
Note: If you come across a spammy tweet, click on respective account name shown on the tweet.
2. Now click on person icon displayed on spam profile.
3. Select Report @username for spam from drop down menu.
Note: Here @username reflects spam account or profile username.
4. Now the suspected spam account will be blocked automatically and report to further review.
Thanks for attention. :D
(Reference)