Hi, and welcome!
Please see the FAQ: What's a reproducible example (`reprex`) and how do I do one? Using a reprex, complete with representative data will attract quicker and more answers.
For this type of general question, it's not strictly necessary, though.
The forecast package has the functionality to do that, taking an argument, h to set the number of periods to be forecast. You'll want to go through the first few chapters of Forecasting Principles and Practice