How to remove this app called “cydia”

After you get done cleaning up the immediate security breach as mentioned above, change your Apple ID password, your device passcode, and all of your other passwords.

Basically, your friend (and one who probably would have just lost themselves that designation around here) performed a massive security breach on your device, and who knows what else happened to your device and your security here.

I’d probably also make a run at the checklists included in the following:

https://manuals.info.apple.com/MANUALS/1000/MA1976/en_US/device-and-data-access-when-personal-safety-is-at-risk.pdf

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

Jailbreaking is against Apple policies, so we cannot assist you beyond providing the link to restore your device.

You are on your own.

As you have already been told, Cydia is a jailbreaking app and you may not be able to remove it. However, unlike the other poster stated, you will not want to use a backup as your backup would still contain Cydia and its remnants. To try and remove it completely, you will need to restore the device to factory and set it up as new, not from a backup. It may require you to use DFU mode, and you will need to look that up on your own. See this about restore to factory. Restore your iPhone, iPad, or iPod to factory settings - Apple Support Ask your friend if he is willing to pay to replace your iPhone since he has voided all warranty on it by altering the operating system. Apple will no longer service that device.

It appears that your friends Jailbroke your iPad. To be frank I wouldn’t be best pleased with them if they did this without asking me. As far as I’m aware, the only fix is to backup (optional, but I assume you want to keep your data), and then restore. There could be other fixes for removing the jailbreak, but you’d need to do some more research on that, as I would think there have been different exploits over the years.

An iCloud backup will backup everything on the phone and would probably end up corrupted anyway. It is difficult to remove that stuff once it is on there, and sometimes you just cannot get it all off.

Whoops, I should probably clarify that I thought an iCloud backup would probably be fine. I guess I’m wrong. As the Pro says, it is against Apple policies…

Any backup of a compromised device is ill-advised. Sorry to say, but the baby must be thrown out with the bathwater this time.