SafeAssign is a tool that runs within Blackboard, and whether or not it is set up in any given Blackboard class shell depends entirely on the instructor. If your instructor has not already enabled SafeAssign within your class shell, We recommend speaking with him/her to see if this can be done. If SafeAssign is set up, you will be allowed to submit one time to it. Multiple submissions will require multiple set ups by your instructor. See the link below for instructions on how to submit something to SafeAssign.
Another option for you may be to submit your paper through some of the free plagiarism checker services available online. Go to Google and type in free plagiarism checker in order to see some of these services. Now, these services will not be as comprehensive or authoritative as SafeAssign, but they can give you a good general idea regarding your paper.
You may also want to review the information in our Writing Help guide (linked below) for tips on avoiding plagiarism as you do your research and writing.