After you enter your W-2 you will come to a screen that says "Let's check for uncommon situations." That screen has a long list of check boxes. One of the boxes says "Unreported tips." Check that box and continue through the interview to report the tips. The unreported tips will be reported on Form 1040 line 1c. Form 4137 will be included in your return to calculate the Social Security and Medicare taxes on the tips, and these taxes will be added to the tax on your return.
In the future, any time you have tips totaling $20 or more in any month, you are supposed to report the tips to your employer, and the employer should include them in the wages reported on your W-2. Then you just have to enter your W-2 in TurboTax, and the tips are already included. For more details, see IRS Publication 531, "Reporting Tip Income."
Did you mean to say that you were told you canNOT report more than $228 of unreported tips? That's not true. There is no such limit. That might be someone's misunderstanding of the $20 per month rule. Tips totaling $20 or more in a month should have been reported to your employer, but if they weren't you can report them as unreported tips on your tax return. You can report unreported tips of any amount, even it's $20 or more per month. But there will be no Social Security or Medicare tax on tips that totaled less than $20 in any one month.