The simple answer is you draw them, but if you provide more information you'll get much better answers.
I have recently purchased the business and all labels currently used have
templates set up. I have had a couple of enquiries about different sized
labels but do not know how to create new cut lines or amend current cuts
for the Summa printer. All very new to me and have a lot to learn. If you
have any suggestions, would appreciate your advice.
I don't know anything about the Summa printer, so I Googled and found one that prints and cuts. If that's what you have, you might want to look to Summa to help with this. If you are cutting after the fact like you would with other printed materials, there are two ways to make cut marks.
One is to set up the page size in InDesign to the finished cut size of the piece, and set the crop marks in the Marks and Bleed section of either the Print or Export to PDF windows.
The other is to set the document size in InDesign to the size of your media and draw a box the size of your finished piece on the page and either draw lines manually or use the Script found in Window>Utilities>Scripts>Crop Marks.
I'm not familiar with Summa printers, but a quick google search tells me thay make a variety of cutting printers for the sign industry (among other things). I'm afraid I don't know what special requirements there might be for file setup, or even if one can use InDesign for making files that are used for output for them.
It sounds like you really need some basic training. For InDesign, I suggest you start with Sandee Cohen's Visual QuickStart Guide to InDesign book, choosing the version that matches your version of InDesign. There is probably also documentation and or training availble from Summa for printer operation. Are the former owners available to teach you? Do you have any employees who have run this equipment?
Thank you for your suggestions. Appreciate the help.