It depends how you have data setup on your iPad, as the newer iPads (iPad pro's 2018, iPad Air 2019, and the iPad mini 2019) those iPads use something that is called an eSIM, which doesn't require a physical sim to receive all of its cellular connectivity.
Newer Model iPads follow these steps:
Step 1: Open settings
Step 2: Go to Cellular
Step 3: Check if your iPad is using an eSIM or a physical sim. (If you are using an eSIM it will say in red "Remove Cellular Plan")
If your iPad has an eSIM, you can remove the data plan there, but you're going to have to contact Verizon to get another eSIM. (If you have a sim card that is not in use that is Verizon branded, then you can use that one and they can activate it for you, you're going to need the ICCID which is written on the SIM card itself, and also the IMEI of your iPad if you're going to be adding it back onto your account this goes for both a physical sim and eSIM
Once you have figured out if your iPad has an eSIM or a physical sim, you are able to follow the next steps.
If you have a physical sim (This will also apply to iPads that are older):
Step 1: If you have a case on your iPad remove the case, and locate a small sim tray.
Step 2: you can use a paper clip or you can use a sim ejection tool to remove the small sim tray from the device.
Step 3 (Follow this if you're going to transfer to another iPad): transfer the sim to a new iPad.
If you want to remove the data line completely from your account, you're going to have to call Verizon, or you can chat with them. (You can chat with them if you click on account>Login/signup)then there is going to be a small Chat with us on the bottom right of the screen. Then, when you have opened the chat window, type "Agent" which will allow you to talk to someone, of which are going to allow you to cancel the line of the data for your iPad.
Things to have ready:
Account holder's name
Having the proper amount of data for your iPad is essential, so let's work together and make sure your device is set up just the way you want it to be.
To begin, can you clarify what exactly you're looking to do with your data? Are you simply looking to change the plan or are you looking to get rid of the tablet as a whole? Is this being billed out on your monthly Verizon bill, or do you pay directly within the iPad on a credit/debit card? We're eager to assist!