This is my first year with Turbo Tax. I need to depreciate assets put in service prior to 2018. How can I get the proper depreciation amounts into turbo tax program?

I suggest you use TurboTax Desktop to do this.  It has a "Forms" option that allows you to view forms and worksheets, as well as make and change entries directly on them.  You will have to enter all of your assets in to the program, and it will automatically calculate current and prior year depreciation.  You can then verify the TurboTax depreciation reports with your prior year depreciation and make any adjustments as necessary in Forms mode.  For more information on TurboTax Desktop see:

TurboTax Desktop Products Comparison

Enter your prior year assets in the Asset topic of your Schedule C.  TurboTax will ask for the Asset information, be sure to enter the information for your prior year asset the same as it was originally enter. This info should be on your prior year depreciation schedule.  Once you enter a date of service before 2018, you will see screens asking if you took any Sec 179 or special depreciation (enter those if you did) and then you will be asked which asset method you used and then ask for the prior depreciation...that's it.

hope this helped!

You do not need to use forms mode...you can do this in TurboTax Self-employed!