All you have to do is reduce that tip income that you are reporting. For example, if you receive a $1000 tip and give bartender $250, you only need to report $750 as your tip income.
When you enter your W-2 form, be sure to select box Unreported Tips when you see the screen Do any of these uncommon situations apply to this W-2... and continue through the prompts. On the Tips Not Reported to (employer name) screen, answer the question about your tips. On the Enter Any Tips You Didn't Report to (employer name) screen, enter the amount of your tips.
This link shows you exactly how to report it... the data entry is immediately after you enter your W-2 form:
https://ttlc.intuit.com/questions/1899731-entering-unreported-tips
If you'd like, more information on tip income:
https://turbotax.intuit.com/tax-tools/tax-tips/IRS-Tax-Return/How-to-Claim-Tips-on-Your-Tax-Return/I...
