If I deleted some drawings from my previous drawings and want to get them back, what do I have to do to recover them?

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just go to deleted items. you will see there the message you previously deleted. then click that message and click recover

restore your system to a period when the drawing was still on your system or check recycling bin

You can try this data recovery program to scan your phone and restore lost data from it.Only a few steps you can get back your lost data from your phone:
Recover Deleted Photos from Samsung Galaxy

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This happened to me before. You just need to delete the app, and reinstall it. Log back in, an it should be fine. However, once you delete it your previous drawings (that you haven't posted) will be gone. Hope this helped!

I suggest you recover all your deleted files and then sort out what you want and then delete the unwanted files before you back up your data.

Recovery software could help you in getting your data back , there are many tools available which can do this for you but you have to be quick with the recovering process, because further delay means that place where your data previously was gets over written by something else. Recover Deleted Text Messages from Android

Yes, it is possible to recover deleted iPhone SMS messages by touching the iPhone mistakenly without backup.

Recover deleted or lost SMS messages with iPhone SMS Recovery tool!

For iPhone 3G/4 users, you can directly recover your lost SMS message back even without any iTunes backup with the help of this world's first iPhone SMS Recovery tool! Just follow the steps !

Unfortunately, there is no such a thing like trash bin on your iPhone so that you can restore your deleted pictures.

However, there is such an iPhone photo recovery software that can help you recover deleted pictures from iPhone 5, 4s, 4 and 3gs. I used Tenorshare iTunes Data Recovery. It worked.

You can give it a shot! You can download it from http://www.any-data-recovery.com/product/itunes-data-recovery.htm