How do I stop someone from remotely accessing my iPad?

Provided that you didn’t install a profile, you’re in a better place than might otherwise be the case.

First, ensure that you only have trusted Apps, that you actually need, installed on your iPad. Review the list of installed Apps here:

Settings > General > iPad Storage

If you see any Apps that you don’t need - or don’t recognise - return to your Home Screen(s) and delete the Apps from there.

Once you have pruned/verified your installed Apps to those that are needed, ensure that you have a current iCloud (or iTunes) backup of your iPad. If necessary, trigger an iCloud backup:

Settings > [Your Name / AppleID] > Backup > iCloud Backup - set to ON - then select Backup Now

When the backup is complete, reset your iPad to Factory Settings:

Restore your iPhone, iPad or iPod to factory settings – Apple Support

The Factory Restore will completely erase your iPad - and install a fresh copy of the most recent supported version of iPadOS. At the end of the Restore process, you can restore your data from your backup; the Apps that previously remained on your iPad, after your pruning exercise, will be reinstalled “clean” from the App Store.

Lastly, and perhaps most importantly, change your AppleID/iCloud password - and complete any post-change actions:

What to do after you change your Apple ID or password - Apple Support

What to do after you change your Apple ID or password - Apple Support

Changing your AppleID password is crucial in protecting your account and your data. You should also verify that your secondary/recovery email addresses - and your trusted telephone numbers - are up to date and belong to you. Access, verify and update your account here:

https://appleid.apple.com

Why would you have called Microsoft about an iPad? Where did you install this app from? Unless you have jailbroken your iPad, you can only install apps from the App Store. The exception is if you install a profile. Did the "tech" have you do that?

Restore your iPad to factory state. Do not reload your back up.

Restore your iPhone, iPad, or iPod to factory settings - Apple Support

What makes you believe that your iPad has been hacked - and is being remotely accessed? Is this just a hypothetical question - or is something more specific?

Provided that your iPad has not been jailbroken, it is highly resistant to malware threats. That said, whilst iPad cannot be “infected” by malware in the traditional sense (i.e. a “computer virus”), as with all computer systems, there are vulnerabilities and threats to which you remain exposed.

If you can provide more information about your concern, or reasons why you believe that you have a problem, a more specific response might be possible.

I believe that you been scammed - using a common ruse employed by some rogue trying to extort money or steal information.

Do you recall the name of the App that you installed? You may find it listed under the “Purchased” section of your account in the Apple App Store App.

Were you asked to install a “profile” on your iPad - prior to downloading/installing this “remote-control” App on your iPad?

Ipad can't be hacked

Unless you have jailbroken your iPad, it can't be accessed remotely. What are you seeing that makes you think that it has been compromised?

Do you remember the name of the app?