Apple will blacklist you if you are using multiple stores that are not having proper Anti-blacklisting methods. tututweak and few other stores have private anti-blacklisting methods to avoid our users from getting blacklisted. This allows our certificates to last longer and our users to use apps for a longer period of time. That's why if you stick to the good stores with good anti-blacklisting, then you can enjoy apps for a longer period of time. However, if you are blacklisted occasionally (which is totally possible) then please follow the following steps if you want to un-blacklist your device.

Delete all the apps downloaded from 3rd party appstores (tututweak, Tutubox, Appvalley etc) Now, do an iCloud backup of your data
Disable findMyiPhone in settings
Now, do this :
Goto Settings
Click General
Click Reset
Click Erase All Content and Settings
Once device is reset, setup as normal and sign in with your iCloud account.
When asked, click Restore from an iCloud Backup option and restore the backup you made earlier
Now Download any apps from tututweak
Make sure to setup NULLIFIED (only turn on Nullified VPN after you have trusted the app in settings else it won't work)