This is a common problem with many devices, it can be due to storage, background apps and or viruses that take up a lot of space.
First of all you need to go to settings and scroll down until you see Battery and Device Care, then you press on it and then click on optimise, your tab should be working a little faster now, then you click on storage and if your storage is above 90% you should probably delete some apps, duplicates, and photos (only if your not using them!) then you should see Device Protection click on it and then you run scan Device (this will take a while) and if your not satisfied you can download Avast a virus detector (it's paid) or McAfee (it's also paid).
That's it! If your device is still running slow you should probably check with Samsung.
