What if my employer doesn’t send me my w2 by the time of January 31st?

Contact your employer. 

Have you asked your employer when they will issue W-2's?  Does the employer have the correct address to mail or send it to you?  Have you asked if they make it available to you on a payroll site that you are supposed to go to?   

https://ttlc.intuit.com/community/income/help/what-if-it-s-february-but-i-still-don-t-have-my-w-2/00/25998

https://www.irs.gov/taxtopics/tc154

@nberrier715 here's what the IRS says

https://www.irs.gov/filing/if-you-dont-get-a-w-2-or-your-w-2-is-wrong